The fact you seemed to easily put on muscle indicates your testosterone is there. There is no normal penis size, so that's a non-issue. The question there is, does it work, not how big it is. We come in all sizes and shapes and maybe this is just yours. But if you're truly concerned, see your doctor and get a blood test for sexual hormones. The thing is, if you were high in estrogen and low in testosterone, I think you'd notice other things as well, such as your voice's depth and if you have body hair (although some of us are pretty hairless, including me). There is something that can cause excess estrogen in children and give them female features, and that's exposure to certain pollutants, particularly petroleum pollution. Oil is highly estrogenic. But again, only a test would tell you that, as it doesn't seem behavior or other factors are showing it. There have been clusters of boys who have gotten female breasts and the like from living near petroleum pollution, so that's a thing. But for a third time, there are blood tests that can tell you if this is just the shape nature intended you to have or is related to levels of sexual hormones.
If you're 17, your body might still be processing all the changes of puberty, and have yet to settle down completely. Evidently man boobs (including soreness) are an issue then, and can be again at age 50 or so. If they stay somewhat larger than other guys,' you could certainly see a doc and get checked. (Test your thyroid, too.)
In case you haven't run across it, here's a good article from the Mayo Clinic:
It might also not be increases in estrogen but instead decreases in testosterone that can cause this problem. Some meds (including some anti-anxiety medications) can cause the problem as well. Check out the article, there's too much info to paraphrase here.
As you say you are over 17, I think it never hurts to get hormones tested. Talk to your primary care doctor about it. I think anniebrooke gave some good advice