I have a rather embarassing question but I really need help. When having anal sex with my boyfriend, after he inserts it and all it comes to a point where it is almost like it will NOT go any further. It's like his penis is hitting a wall of some sort and it really hurts. I am very relaxed before we start so the initial penetration is not a problem at all, it's just that there is something stopping his penis from going all the way in. what is causing this and what can I do about this?