I wonder why?

Okay so i had sex the other day but i read that when having sex boobs become sensitive and bigger and swollen but yesterday i noticed that both weremy nipples were swollen and still are swollen i took a pregnancy test and it came put negative why else woul they be swollen......my boyfrined think he made them like that from sucking on them.....if so how long do they stay swollen i need help and advice please....