Is my body rejecting absorbing stitches? I've been on antibiotics for a week. Should it be calming down if was an infection?

Without seeing you in person, it is difficult to say for sure. Often a small wound breakdown at the "T" goes on to heal well with conservative management.  Redness, and pain may suggest an infection.  Best to check it out with your surgeon.

I am sorry you are having trouble with your operation.In general if you are allergic to absorbable stitches or just sensitive, the reaction would happen all along the suture line, which it sounds like it hasn't, so I don't think you are allergic to them. Most dissolvable stitches take 3 months to dissolve completely.You have a dehiscence at the T-junction, which will heal in time.I am unsure whether it is your incision only or the breast around the incision also which is warm to the touch and red, but yes antibiotics should calm it down, if it is an infection and the correct antibiotics. It can also be fat necrosis, which will subside by itself and is not an infection. If there is no change after a week of antibiotics, please go and see your plastic surgeon.