Hi. So, I've Been With My Boyfriend For A Little

Hi. So, I've been with my boyfriend for a little over a year now. The sex has been great. We saw each other almost every single day and often did "it" more than once a day. Recently he got a full time job. We now see each other at most twice a week and have sex once a week. Drastic change, but that's not the main problem here. The last couple of times we've had sex, after we finished, my vagina immediately felt sore and swollen and hurt a lot to the touch. The first time it happened, there was also a tiny amount of blood. The pain would also last for a few days. Just yesterday we had sex again. I felt a little pain at the beginning, it went away during, but immediately came back strong when we finished. Today, the pain is gone and there isn't any soreness. I know it can't be an std. My boyfriend and I are clean. Can this just be a problem with lubrication?