During my puberty, I had gynecomastia which caused a lot of breast/nipple development. The doctor said I had to much testosterone which my body was converting to estrogen. It was very painful. Many years later, I'm now in my 50s, HRT, has caused my breasts to get fuller, heavier and my nipples to protrude more. I have not experienced the same nipple pain as during puberty. I'm at least a 40B. Like Ashley, I feel them now when I do things. I enjoy the bounce when I walk, etc, however, running I need a sports bra. my wife and daughter comment on how much they have grown. I wish I had taken a picture before I started. So, I believe HRT is continuing what my body started a long time ago. I hope this helps.
Deanna