Advice please!

Hi so about a week or ago I had sex with a guy and ever since my lower abdomen has been in pain and will burn. I figure it may be acid or something in my stomach. But the pain in my stomach comes and goes, especially when I eat but now I just feel burning. I've taken acid medicine and it's helped alittle. My period isn't expected for 7 days but ive had it come a week early before so that wouldn't be uncommon. I'm not on birth control but I do use condoms. The last time I had sex was painful as well and my symptoms returned after being gone for a few days. Any suggestions on what wrong?