I am 18 and so is my girlfriend. We haven't had sex, but everything else leading up to it. The reason why we can't do it puzzles me. She is too tight, my two fingers hardly go in there let alone my penis. Help. How/what can I do?
First, if your partner has not had a gynecological exam and full STI screening recently, she should start there. (If you haven't had a full STI screen recently either, you should do that as well.) Since the two of you are sexually active, you should both be getting regular sexual health care. Some STIs or other problems can make penetrative sexual activities difficult or painful. It is best (and easiest) to rule out any physical problems or infections as soon as possible.
Next, is your partner relaxed and aroused when you are attempting intercourse? The vaginal canal is a muscular tube that is basically closed (the sides touch one another) when nothing is inside it. When a woman is aroused, it will relax to allow for comfortable penetration. So if your partner is not thoroughly and fully aroused or does not want to be engaging in penetrative activities at that moment, that could be causing difficulties. The simple fix for this is to make sure that you are engaging in activities only when you both want to and to make sure that you are taking enough time to engage in foreplay and/or other types of sex so that she is aroused when you attempt penetration. (If you are not using lots of extra condom-safe lubricant with your condoms, adding that to the equation may be helpful as well.) Also, other concerns can contribute to problems becoming relaxed and aroused, like concerns about pregnancy, STIs, getting caught, etc. So if you have not addressed those issues, you and your partner should do that as well.
Finally, I'd encourage you to remember that intercourse is not the be-all-end-all of sexual activities. If you cannot engage in penetrative sex right now, that's ok. Generally speaking, intercourse is not exclusively satisfying for most women anyway. Usually some other form of stimulation is needed as well. There are plenty of other things that you can do that are pleasurable for both of you. So there is no need to stress or pressure yourselves into having intercourse right this second.
You can also check out these links for more information: