Does anyones nips show thru a sports bra or is it b.c my breasts are relly small and i have no boobs to fill it out what should i do when im swimming to hide them?

No it doesn't have anything to do with the size of your breasts. Sports Bras most definitely show nipples. What i advise you to wear is a padded cupped bra with underwire, (you could go to wal mart, lasenza girl, lasenza, or Victoria secrets to get your bra size measured) the underwire helps support the breasts as it grows so when you're old it won't be droopy and saggy. As for the swimming part, alot of peoples' nipples show when they're swimming because in the water, you get cold and just like goose bumps your nipples raise up. One way to hide them is to buy a padded breast area swimsuit, you can get a cheap one from wal mart, or even department stores. That way no matter how cold or how much your nipples show, they won't!