For the transgendered woman, breast development will vary greatly, as it does with the genetic female population. However, breast development will typically be less than what is experienced in the genetic female population.
With the transgendered woman, breast tissue growth is basically promoted by oestrogens and anti-androgens.
At 6 weeks into HRT, you should (maybe, probably) be noticing some breast development:
After about six weeks of hormone treatment, subareolar nodules may be felt and the nipple becomes sensitive. After about three months breast buds may visibly start to form. There is an elevation of the nipple and surrounding breast area as a small but increasingly obvious mound, and the areola diameter may begin to enlarge.
At six weeks, we are sure you’re sensitive / tender / sore (I know I was!) Breast tissue is starting to develop, but most of the mass you have at this point is (most likely) whatever fatty tissue & muscle you started with. And, of course, whatever fatty tissue your new hormones are encouraging your body to store in your breasts that it wasn’t storing there previously.
You may see the size of your breast remain the same for an extended period of time even while the composition (and potentially shape) of your breast changes. You may have had well developed pectoral muscles that will atrophy as an effect of anti-androgens. You may lose fatty tissue at the same time other structures of the breast develop.
In the first year of HRT would see a lot of changes. Your body, including your breasts, will continue to change as time goes on. What size you end up with will depend on a host of factors that include age when you start HRT, the specific HRT regimen you’re on, genetics, and several others.