If you can find a tape measure, check your thighs, calves, hips, waist(just above your hips) .. probably every two weeks or so.. and write them down... You'll be able to chart how you're changing.. Your breasts are getting a combination of fat redistro, and cell dividing/growing.
How long have you been on HRT? Some begin their changes right away(within a few days) some after a few weeks, some.. Months... Everyone is different.. your breasts will def ache/itch/hurt as they begin to grow, your butt will ache if you sit on hard chairs/stools.. but likely, as Michelle said, your normal jeans will start to feel tighter, fuller, or just not fitting right again. My guy jeans (Levi 505s were all I wore) stopped fitting right after abt a month.. I started going to Goodwill for girl cut jeans... Aeropostale, Gloria V'bilt started fitting much better, and at abt $4-$5 each, already broken in, wear much more comfortably than my guy jeans. Just be ready to have to figure how to carry all your stuff because the pockets are soooo much smaller than guys pants. There's just no room for more than $6, a tube of Chapstick and a iphone