Painful Intercourse?

Hello ladies, I'm 19 years old and just moved in with my boyfriend about 3 months ago. Things have been going pretty well, except sex. I have never experienced pain before up until about a month ago. I have done extensive research and have only found the same things over and over. Some of the causes I have found are trichimonas, low sex drive, and just not being into your partner or feeling comfortable around them. While these are all great explanations, none of them fit me. I was tested for trichimonas this year and the test was negative so I know that's not my problem. The other problems don't seem to my problem either. Has anyone else experienced this or know someone who has? Please leave suggestions. Thanks girls.