Since you are working out on a regular basis and your body is still developing I think that there is no need to be worried and if you continue with the gym and healthy diet everything should be just fine. In your age I had similar problem and since then I have started with the gym and it has been for about 12 years now and I am happy that I am leading this type of life.
Considering the other part of your question gynecomastia is the enlargement of the male breast and this is resulting from proliferation of the glandular component of the breast. It's from altered estrogen-androgen balance or increased breast sensitivity to normal circulating estrogen level.
But it is not likely that you are suffering from this but if you want to be sure consult your doctor.
Breast and nipple style, like other physical attributes, vary from individual to individual in both males and females as I'm sure you know. The way your nipples look is only an issue if you think it is (although I agree with Neron above, that if you are really concerned from a health perspective, you should seek advice from your doctor). In fact, many of both sexes prefer "puffy" nipples, and find them intriguing and exciting. Try not to be self-conscious about them if you can -- some would consider them a gift!