Swollen vaginal opening?!

Swollen vaginal opening?

This might be too explicit. Please don't remove my question. I need answers.

I had sex with my boyfriend less than two hours ago. I've only had two sexual partners. My ex-boyfriend has no history of STDs, and so do I. My current boyfriend also has no history of STDs. Our last testing date is less than three months ago. I've noticed that after sex it burns to pee. I've had lots of urine tests to see if it is a UTI but the tests came back fine. I've had problems with this before so my doctor told me that I should urinate after sexual intercourse. He's faithful and so am I. I noticed that my vaginal opening is swollen. This happens everytime I have sex. It is not a latex allergy because we don't use condoms, but the pill. Why does my vaginal opening get swollen? Is there anything I can do to prevent this in the future?

This happens to most women after they have sex - it's common. It is more noticeable when you are relatively new at this sex thing so go a little easier. If it is very bad and bothers you or is painful an ice pack (ice cubes in a plastic bag - then wrap it in a thin washcloth) will help.
The urinating BEFORE and AFTER sex is to keep you from getting a urinary tract infection. And it is a very important practice. Remember to do it.
And in the future you should always use a condom - whether you're on the pill or not - unless you are really with someone. Being on the pill will not protect you from anything but pregnancy. So unless you two are really committed to each other - like for life - do not stop using condoms.