5 days post op Breast Reduction, I started getting terrible rash. Any suggestions? (photos)

I don't think this is an allergic reaction, it is misleading the focus, it is much likely a deep fat necrosis, very soon you may experience oily discharge with bad odor, do address this issue to your surgeon.Free acids after adipocyte rupture is an acid substance, therefore "burns" or irritates the depth of the breast and finds the way out through the wounds.Takes time to be solved, spontaneously or with drainage by the surgeon in his office.If not properly managed you can end with serious infectious problems.

The most common cause of skin allergy is adhesive (tape etc.) or antibiotics (oral or topical) after breast reduction.  It sound like your surgeon is managing you properly so you should see improvement quickly.

Severe post operative rash needs aggressive steroid treatments (IM or IV). Plus local care to areas.....

Though we cannot diagnose from a photo, your rash appears to along areas where adhesive might have been placed. We would treat this by removing the tape and cleaning the residue with Ivory soap, and we prefer topical hydrocortisone ointment rather than oral medication. Keep in touch with your surgeon, and your dermatologist migh be a good resource as well.

I think you may have an early infection called cellulitis If  you don't have the the other doctors said but see your surgeon.