Why am I sore and sometimes swollen after sex?

[{?}]

I've been with one man, and we've been together for over 3 years. After a year and a half of having amazing sex, something happened and for some reason my vagina gets swollen. I've put on about 10 pounds since we started dating, but I'm only at 118 lbs max. I can't have sex for more than a few minutes without it getting sore and starting to burn, I think it has something to do with it maybe not being wet enough, but we've tried so many different kinds of lube. Even putting a tampon in anymore kills. This may sound weird, but it use to be so wet and tight, but now it's just tight and doesn't get very wet anymore. I want to start enjoying sex again, but I'm having difficulties. We've tried different positions, different locations, fooling around, and just about anything. The first time it swelled up I could barely walk, it hurt to pee, and the lip were so swollen I couldn't put my panties back on and had to ice it for over an hour. Any suggestions? I'd really like to start having sex like we use to, which was once or twice a day minimum.