HELP! Belly pains

It might be a stupid question, but me and my boyfriend had sex on Monday night (unprotected as we are TTC) and it's now Thursday and I am having the worst stomach pains I have ever had and all of my sides are sore, it isn't a pain that's telling me it's toilet time (lol) and I took a pregnancy test just out of curiosity but they came back negative. Can anyone give me pointers for if I might be pregnant but it just isn't showing up yet!?