So I'm 4 months on HRT but honestly mine started filling slightly during the three months prior when I was using things like flaxseed, mint tea, and saw palmetto to reduce my T levels. So to my situation into perspective, I have had low T in general for about 7+ years anyway. During that time I had really slow tissue growth start. First just a bead under the nipple. Then it was under the whole areole. Pretty much as far as it went. When I limited my T more with diet I started getting aching in the breast area. I also started loosing more muscle mass pretty quickly in those months. The aching radiated outward from the tissue under the areoles.
I then started low dose E, spiro, finesteride for 3 months. This is after my therapist wrote the letter and I got to see my endo. During this time there was more of a constant aching. They definately grew some. A month ago I got a full dos of E and added P. The first three weeks the nipples were very painful to bump. Like super painful!

They both got really firm under the areoles. At some point this started expanding outwards. It's kinda strange how they go from small to being quite noticeable pretty quickly. Only a high support sports bra keeps them close. A regular comfort type bra and they look just like another girls boobs.

Hopefully they will keep this up so at some point they more match my frame size.
I think they grow in stages. Like they grow more under the nipple area then for a while slowly fill. Then repeat again. Yeh and so my left is bigger than my right. Eh what you gonna do?