Well I'm not on HRT (other than what my body naturally produces as my T declines with age). But back in 2014 at age 61, for the entire year, my left breast ached and was a little tender (I'm sure it was far less than what you ladies experience). I got so excited and hoped for some gynecomastia. Alas, only a little development happened, although my left nipple did get infinitesimally larger. The right one never did participate except briefly.
Now to Donna's mention of doing pushups, I participate in a weight lifting class (Body Pump) at the YMCA twice a week. It's 80% women BTW. Anyway, the chest exercises (bench press, butterflies with dumbbells, push ups) have done wonders for my pec muscles and I have pretty nicely shaped "breasts" from that. Small, but they look decent under the proper shirt

So anybody who's wanting more up there, I can recommend this approach (it's taken several years however).