HELP!

I have never organismed and I want to so badly. I'm on baby #2 and I've been with my hubby for 3 years. How do you do it? I get really into it and feel like my body is about to explode but I get scared and make him stop but it's just like a natural reflex I have. I have to make him stop. I'll do anything to make it stop but I really don't want to. I want to O. Tips? Anyone know what's wrong?