Puffy nipples after first day in the gym. Could you please advise if this is something I should worry about ?

It is very hard to know why you would have recurrent puffiness of the areolas a year after surgery if there was no problem until the workouts started. My best guess is that the workout caused a modest amount of swelling, however there is no way to know for certain without examining you. I would recommend that you see your original surgeon to assess what is causing the recurrent areola issues.

 Increased swelling with exercise is not uncommon after surgery but because you are out well out of the healing phase is best to schedule a follow-up examination with your surgeon To make sure everything has healed well.  

you almost certainly had an incision at the lower half of your areola. It is just some swelling related to exercising. don't worry about it. keep exercising. It may take even a few months for the swelling to go down. It is very unlikely to be anything that requires any treatment.david berman md