I have swelling on my sternum 3 week post op. Is it normal and is it going to subside, or is it symmastia? (Photo)

I am afraid you have a serious complication, symmastia, and you'll need future repair with a very very good surgeon who is truly profficient in capsulorraphies and, if available, polyurethane coated implants.By the way, I wonder if you were told you had tuberous breasts.

Based on the photo that you posted, it looks like you may be developing symmastia.  You should go in and see your plastic surgeon, as a physical examination is the only way to know.