Could this be an allergic reaction after my breast augmentation a month ago? (Photos)

It does look like some kind of allergic reaction.  Have you changed detergent or soap recently?  You do need to reach out to your PS though.  You may be able to send him or her these photos and he or she may be able to determine a cause based on your medical history and photos.  At the very least call and let them know what is going on. 

This rash around your incisions appears to be an allergic reaction. Before applying any creams to this area, contact your plastic surgeon for further direction. If you are hours away and are not able to come in for an in-person evaluation, often you can send these photos to your surgeon for evaluation and advice. As always, continue to monitor this area for increased redness, warmth, or drainage as these can indicate infection. 

Hello,
It seems to most resemble an allergic skin reaction, and less like a fungal rash.  You can begin OTC Benadryl (which will help with the itching).  Don't be overly alarmed, but I do recommend contacting your plastic surgeon who should have a mechanism in place for patient contact even over the weekend.  Your plastic surgeon will be able to better direct you with your wound care.  Good luck.
ABPS board certified plastic surgeon