RAW, the only mention of damages in the spell description is:

 > If it enters a space with a creature, it stops moving for the round and deals 3d6 points of fire damage to that creature

So you wouldn't take any damage, unless Wizard moves the sphere back and forth so it enters your case and stops on you. I guess in this case you definitely should start asking questions.

However, this line:

 > The sphere moves as long as you actively direct it (a move action for you); otherwise, it merely stays at rest and burns.

suggests that the sphere keeps its hot and flaming aspect even when not moved by the wizard, so making a houserule would be legit. I suggest to rule it as : 

 > If something enters the flaming sphere's space (for example if someone is bull-rushed in) he immediately takes 3d6 points of fire damage (Reflex negates).

 > At the end of the caster's turn, everyone who is inside the sphere's space takes 3d6 points of fire damage (Reflex negates).

 > The sphere don't do damage when entering someone's space anymore (but still stops and thus will probably do at the end of the turn)

	
I have seen someone using the spell like that in a game and no one even noticed about it not being rules-as-written. I just discover today that it doesn't work the way I thought (and I find the official way less intuitive).