I've cut the end of my penis while having sex.

Hi, im a first timer at these forums, and i needed some advice without consulting my doctor at the moment. Im 16. About 4-5 weeks ago now, maybe a bit longer, I was having sex with my girlfriend, and without realising, due to having such a good time, she wasn't as easy to "get into." Now i've damaged the end of my penis. The urethra is fine. Its the foreskin around it which has a cut on either side. This has happened twice now, it had healed before, and i've managed to do it again. Im contemplating telling my girlfriend, but i don't know how she'll react, we regularly have sex and i don't mind as such wearing condoms, but i'd rather not. Is there anyway i can avoid cutting myself like this, due to this stopping me from having sex, Its as if the Inside of my penis comes out of the hole at the top and stretches it and cuts me.


Thanks for reading, please respond asap.
Mike