Hey, I've worked with lots of folks over the years as a nurse in primary care and before that as a youth group facilitator and this is one of the most exciting periods though often frought with a lot of complex emotions as we undergo hormonal change, physical changes (some of which you describe), and significant social changes as how we are socially read can become more 'visible' and challenging before (and I hate to use the phrase but it's largely true) it gets better. All of those changes can beget strong emotional changes that can be difficult to ride out and be patient with. Though a challenge sometimes, I'd encourage you to enjoy and savour this magical time, of relatively rapid (though it feels so slow) physical growth as you've made the decision to give yourself the joy of a second puberty! Good on you girl! :-)
To answer your question, breast development can start anywhere from 1 week to beyond a month of having started hormones depending on our unique biologies which are shaped by age, genetics, and body weight, primarily (pharmacokinetically, estrogen responds better when we have more fat to begin with). The tenderness, though maybe disconcerting, is likely normal. At this stage your family doctor or nurse practitioner (or whoever is prescribing you hormones) should be doing bloodwork at least every 3 months to check your hormone levels including prolactin which can often be elevated in the weeks to months after surgery. Let them know if you notice any milk or other discharge (while it may not necessarily be a problem, they should probably know about it).
One thing that I've noticed is that there is such incredible variability with respect to breast growth and development and the timing thereof. For myself, I had some good growth for the first year or so that I was on estrogen (and anti-androgens) and then another spurt shortly after my orchiectomy a few years. I was a decent A but I had quite pointy, almost tubular breasts. Over the past 2 years or so (this is well over a decade on hormones and now in my mid-30's) I have undergone another significant growth spurt and I can't quite figure out why this is the case, but it's happened and now, finally, my breasts are almost a C most days and much more mature and full. Go figure! All this to share an example of how things can shift and change even beyond the "18-24 month" window that is so often thrown out there (by us nurses and other providers as well as community members) to delineate the period of most significant growth. I caution all people to wait at least that amount of time before considering implants and even then, if your hormone prescriber thinks its appropriate to try adding micronized progesterone to your regimen and/or increasing your estrogen dose for a time being as these can occasionally help but also carry their own risks.
Good luck with everything!
Rebecca
Toronto, ON
35 years old
Transitioned socially 1997
Hormones since 2002
Orchiectomy - Toronto (Klotz) 2005
GAS (vaginoplasty) - Montreal (Brassard) 2008
FFS (forehead/nose) - Buenos Aires (Rossi) April 20, 2016!!!
