i can't get preganant no matter what i do.

i am 19 years old i am trying to get pregnant for the last 3 years but it never seem to happen. i have unprotected sex with all of my boyfriends and they all came (sperm) inside of me but i never become pregnant. i am wondering if it was because of the reoccuring pimples that i have on my vaginal area that contain puss, sometimes i pass some yellow substance and it smells bad and the pain that i have experience in my belly. could this all be affecting the ability for me to become pregnant or could it be that i haven't find the right guy as yet. i am really scared because i really want to get pregnant and have four beautiful and healthy childern. :'(