Low grade fever post breast augmentation. Should I be concerned?

Most likely this fever is coming from some collapse of the air spaces in your lungs because you are not taking deep enough breaths.  If your pain control is inadequate, it will cause you to splint, which does not expand your lungs enough.  If there is no redness on your breasts to explain a fever, then the first guess is atelectasis (lung space collapse).  This is easily remedied by taking deep breaths and expanding the lungs.

Elevated temperature after any surgery may be something serious...or nothing at all. It would be wrong for any of us to give you advice about what may or may not be a potentially serious issue. The best thing for you to do is to call your surgeon NOW, and be seen so that he/she can evaluate you and determine if this is something to worry about. 

Fever early post-op is fairly common. If it persists, then it needs to be evaluated by your doctor in person. Best of luck.

It sounds like this is probably a normal postoperative response. However, without interviewing you further and then examining you it is impossible to rule out a more serious cause for your temperature. Call you surgeon and discuss this with them without delay.