I have developed a rash on my armpits 2 weeks after my breast augumentation.

Thanks for your question! This is not entirely uncommon, and is probably just a topical yeast infection. It can probably be alleviated in 1-2 weeks with topical nystatin cream. However, check with your plastic surgeon (have them physically see you and look at it) just to make sure. Best of luck to u!

This is most likely Candidiais so mycostatin cream with help.  If not, try Lamisil cream which is more for mold rashes.