Constant yeast infection !! 16!

I'm 16 years old and so far I've had 3 yeast infection this year and 1 currently. 1 was from wearing tight clothes ( I stopped) the next 2 were right happened right my boyfriend came in me ( he stopped now ) and now I have a current one 2 days after having unprotected sex. I'm not sure what to do . I have the IUD and I'm not sure if that might be the reason for it happening constantly. Help ?.. or am I just prone to getting it