I'm afraid to have sex

My husband and i use to have sex all the time...just about three times a day. But recently i have just gotten this fear of sex. Just the part where he goes in me, so i try and avoid it. I know that's not good but i just can't help but to feel this way. When i was 14 i was raped and for some reason now i think of sex and connect it with pain. I don't understand why after 6 years and 2 years of marriage I'm starting to be afraid of having sex. I want it all the time but the fear holds me back and i end up masturbating. Now that i want kids....how am i suppose to have them if i can't even have sex. Sometimes the fear passes but it sux when i have to wait two weeks for it to go away. What should i do?!