what is my problem?

I've been seeing my boyfriend for over a year now he took my viginity but everytime I'm having sex with him I just flip out of the mood suddenly, I see him as a perfect man n he's good at knowing how to touch me but I just keep blocking away the feeling, I love my bf n he loves me with all his heart but I still aren't accustom to sex yet is it because I'm only 18 or because in my country parents only want their children to have sex wen their married, guys please help me I truley love my bf bt wats my problem with sex