Whats that smell?

This is so embarrassing, but i just think i need some thoughts. Ive been dating my bf for 3 months now, we've been having vigorous sex. But I've notice every time he ejaculates in me, my vagina has a instant reactions within hours it starts to smell like fish... which then turns to thrush... im not sure what to do... he doesnt seem to think its him causing it... and i know ive also never experienced this either... Has anyone had an experience like this and what did you do to cure it.