Do you experience any pain when you have sex using a condom? If you have never used a condom, you should try it and see if that helps. I do not think you are allergic to his semen. In your post you stated that you experience pain during intercourse even before he ejaculates. If his semen was the only problem, then there would be no pain until ejaculation.
It could also be an issue of you being too dry. Your body should naturally produce plenty of wetness for sex. You may need to linger over foreplay and not have sex until your body is ready for it. You could also buy a lubricant such as KY jelly.
If the condoms or lubricant don't help, you should speak to a gynecologist about this. It is not normal for intercourse to be painful.

i read a lot of post that complain about the same thing. i think you should use condoms. i used condoms with my ex of 5 years faithfully. and if you are having any other discomfort use ky-jelly to see if that helps you.
make sure your b/f is gentle and do not let him enter you if you are dry.