Why does it hurt after fat injecting in my chest? 3 months post op. (photos)

Thank you for sharing your question and photographs.  Based on your narrative you had fat grafting performed of your chest to help correct a contour deformity.  Unfortunately it sounds as if the area has recently been compromised with an infection requiring drainage by your surgeon and antibiotics.  It sounds as if you are receiving appropriate treatment and hopefully the transferred grafts have taken and are strong enough to resist the infection.  maintain close follow up with your treating physician in order to make sure your heal appropriately. 

Well this certainly is not normal, but it is a potential complication of any surgery.  It sounds as if you developed an area of fat necrosis (fat that did not take) that may have become infected.  Areas of fat necrosis can be red and tender even in the absence of infection.  It sounds like your surgeon is treating you appropriately.