So I'm building an evil half-orc barbarian with a rage tree on biting and eating an opponent still alive. When I get multiple iterative attacks from a high BAB, will I only be able to make a single bite attack? Even if I can't use more than one bite a round, can I still use a weapon? This might greatly alter my build if I can't find the answer to this.
A creature that makes a full attack is usually limited to making one attack with each of its natural weapons in addition to attacks because of its base attack bonus
You do not receive additional natural attacks for a high base attack bonus. Instead, you receive additional attack rolls for multiple limb and body parts capable of making the attack (as noted by the race or ability that grants the attacks).…
Creatures with natural attacks and attacks made with weapons can use both as part of a full attack action (although often a creature must forgo one natural attack for each weapon clutched in that limb, be it a claw, tentacle, or slam). Such creatures attack with their weapons normally but treat all of their available natural attacks as secondary attacks during that attack [hence typically suffering a -5 penalty on attack rolls and a bonus on damage of only half the creature's Str bonus], regardless of the attack’s original type. (Emphasis mine.)
And to clarify, Full Attack, in part, says
If you get more than one attack per round because your base attack bonus is high enough (see Base Attack Bonus in Classes), because you fight with two weapons or a double weapon, or for some special reason, you must use a full-round action to get your additional attacks. (Emphasis mine.)
And, for many PCs in particular, having a natural attack is one of those special reasons.
Thus when a creature has a claw attack or bite attack or another natural attack, the creature can take a standard action to make a standard attack with one natural attack or make an attack predicated on its base attack bonus. Further, such a creature has the option, when making a full attack, to make its attacks predicated on its base attack bonus normally and, if it wants, also make a secondary attack with each of its available natural weapons.
So a level 1 barbarian with a bite attack can take a standard action to make a standard attack with either her greatsword or her bite attack. Alternatively, that level 1 barbarian could take a full action to make a full attack attack with her greatsword and also employ her bite attack once as a secondary attack.
At level 16, that same barbarian can take a full action to make a full attack—therefore up to four attacks—with her greatsword and also employ her bite attack once as a secondary attack. However, even that mighty barbarian cannot normally make, for example, two or more bite attacks during a full attack.
In short, unless an exception applies, a creature just can't make multiple attacks with a natural weapon, no matter how high the creature's base attack bonus.
See this question for more information about making a full attack using both base attack bonus and natural attacks.
Note: This answer deliberately avoids listing the multitude of exceptions in favor of weasel words like usually and normally. The writer begs the reader to generously pretend that those words address the reader's favorite exceptions (like, for instance, pretty much everything involving unarmed strikes). Also, this answer leaves it to others to assess the viability of a biting barbarian. While this player is experienced with monsters biting his PCs, he has little experience with his PCs biting the monsters.
Normally, you can only make one natural attack with each natural weapon you have per round.
You can full attack with a regular weapon (or unarmed strike, or what-have-you) and then make one attack per natural weapon, taking a -5 to hit with each natural weapon attack (using your full BAB - so if you were at BAB of 6, and had a strength bonus of +3, each natural weapon attack would be at +4 to hit (6 BAB + 3 Str -5 (secondary natural attack)) which is referred to as using your natural weapons as 'secondary natural attacks'. These secondary attacks also only add half your strength to damage, rather than full strength. You can also make one 'primary' attack with a natural weapon and then as many secondary attacks as you have other natural weapons.
This could be something like grabbing someone, biting down on their shoulder, and then punching them in the gut 3 times with a dagger before ripping away their flesh with your bite. It could also be the common claw/claw/bite attack routine.
However as a GM I have houseruled that natural weapon attacks can be used in place of a regular weapon to perform a full attack in situations where a PC (or prominent NPC) has a natural weapon they wish to use as their primary attack and have a BAB high enough to full attack and are a humanoid or otherwise not a traditional 'monster'. Most monster statblocks that rely on natural attacks have enough attacks to make up for not full attacking, or very powerful attacks or stats to make up for their lack of iteratives. If a Tiefling Paladin wants to use his native claws to slice and dice people it makes more sense to allow him to gain his iteratives from BAB than to not allow that, as he could do far more damage with a greatsword and the lack of full attack is just insult to injury.
I have also witnessed many tables allowing natural attacks to gain iteratives when used by PCs (although not usually by large monsters or the like, instead just using whatever attack routine is listed on the statblock), either unaware of the rules on how natural attacks work or having houseruled it (either explicitly, or the GM has just behind-the-scenes houseruled it with the players none-the-wiser).
I would suggest in this situation that the GM of this barbarian consider such a houserule, as a bite attack has a lower damage dice than any two-handed weapon and benefits less from power attack and strength. Two greatsword attacks are going to do more damage than 2 bite attacks, even if the barbarian optimizes to some degree and adds two secondary claw attacks on top. In general even if it does allow some greater degree of optimization, allowing player fluff to work out mechanically is usually far superior to otherwise, and this isn't even one of those situations at all.