You can only have one bonus action per round. (and only one action, and only one reaction).
And to add to this and clear up possible confusion (or possibly create some), you can't use your bonus action as a regular action. Bonus actions are bonus actions, and actions are actions, and ne'er the two shall meet.
Example: monk/cleric (or Rogue/Cleric - class doesn't matter as long as it allows Dodge as a bonus action for this example) uses Ki to Dodge (bonus action). He then uses his move action to move toward his comrade (unconscious), to get within range of his Healing Word spell. Note, he still has his action, and wants to use it to cast Healing Word (bonus action) instead. Can't do it.
The relevant rule can be found in the PHB, pg 189 under YOUR TURN
On your turn you can move a distance up to your speed and take one action
followed by the subsection immediately below under Bonus Actions
You can take a bonus action only when a special ability, spell or other feature of the game states that you can do something as a bonus action.
and in the following paragraph...
You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.
And, since I mentioned it above the relevant note for a Reaction is on page 190 of the PHB under the Reactions section.
When you take a reaction, you can't take another one until the start of your next turn.
Finally, my note about not being able to use a bonus action as an action (more applicable to spellcasting than anything else) is referenced in one of the early Sage Advice columns by Mike Mearls and Jeremy Crawford (Sept 2014)
Q - Can an Action be a Bonus Action? i.e Can a Bard use a BA to grant Bardic Inspiration and an action to cast Healing Word? A - Actions and bonus actions aren't interchangeable, so that bard could use Bardic Inspiration or healing word, not both on a turn. -J