Storing fat in the chest is not feminine for men. In fact, the first two places in a man's body targeted by fat is the chest and the abdomen. What would be called feminine fat distribution in men is fat accumulating in the buttocks, thighs, and legs. That's why it's very common to see chubby men with hung bellies and big breasts, but with normal-sized thighs and legs.
Prolactin only causes gynecomastia when there's associated increase in estrogen. Elevated prolactin alone causes galactorrhea (milk secretion in males), not gynecomastia. However, you still should get this hormone and others checked. The important hormones in this case is:
- Testosterone
- Estradiol
- LH
- B-HCG
- Prolactin
As to your question about the feminine hormones and losing weight, firstly, not because you have excess fat in your chest that means you have excess estrogen. As I said fat normally gets stored in the chest in men. The hormones work-up will tell you if you actually have excess estrogen which could be the cause, which is unlikely because you're overweight, and so the fat on your chest is part of your obesity. Secondly, it should go the other way round, losing weight decreases the levels of estrogen or at least lowers its efficacy. If you're through puberty (12-18 years old), I'd try to get in shape and lose as much fat as possible. This increases the chance of both the fat and the gland going away. If you're out of puberty, working out will decrease the fat portion but not the gland.
Hope this helps.