I Am Getting Bit By Something. I Don't Know What.

I am getting bit by something. I don't know what. I have 5 bites. 3 on my leg all next to eachother, and two on my butt. They do not itch at all. They just hurt really bad and swell up. This seems to happen to me every spring. They swell up very large and can be extremely painfull. I have looked for bedbugs but cannot find any. I really need to find the culprit, I would like to be able to where shorts without giant red swollen bites allover my legs. Please help :(