If you are consistently sore after intercourse, you can try a few things:
1. Go slower. Ask your boyfriend to move his penis inside-to-outside of your vagina slower or more gently, as the "friction" may cause soreness if sex is too fast.
2. Increase foreplay. You may need more time to emotionally and mentally prepare yourself (including your vagina!) for intercourse. Don't undermine the power of your mind and emotions during sex, and speak openly about what you need/want.
3. Increase lubrication. Both of the suggestions above could increase your natural vaginal lubrication (the most important aspect in preventing soreness!!), but if neither of these techniques work, you can purchase OTC (over the counter) personal lubricants such as Astroglide or KY Jelly in the same aisle you find condoms.
4. Communicate. Be sure you are in the mood for intercourse, you are ready at that moment, and you can stop at any time. You would need to have this conversation with him before any physical intimacy begins!
The mind is such a powerful sex organ, that If in your mind, you know that your boyfriend will not be disappointed or mad, and will essentially be OK if you say you need to stop having sex, that your body may respond during future sexual encounters with less soreness and more lubrication. Give it a try! It may take awhile for your body to be reassured that it is not about to be injured or hurt (just speakign from your vagina...not saying there is intentional physical hurting, just that it is hurting), will help break the current sex-soreness cycle you are in, and begin a new positive cycle.
Does this all make sense?