i noticed that in the shower, my nipples are puffing up. they've never done this before, but i've been on estrogen since late august. anti androgens since march. is this a sign of breast development?

Yep, sure sounds like early stage development changes to me! The area around my nips was one of the first things I noticed.
Randi

Yes, generally during the first stage of growth the nipple will start forming a mound behind it and look puffy... They usually will become itchy and rather tender to the touch with each growth spurt

Sounds like your on your way

Congrats