My cycles are usually 24/26 days long and my period lasts about 7 days. Had unprotected inter course the last dayof my period. Cramping ever since. 6d?

Probably normal. Each month when you ovulate, there is a cyst on one of your ovaries at least 2 CM in dia. That cyst starts to develope while you are having your period, and continues to enlarge until you ovulate - in your case about 10 or 12 days after your last period started. 14 days later, if you don't conceive, you will start your next period. That cyst may enlarge, up to 6 or 8 CM and may cause your cramps.
See your doctor. I would be concerned that you might have a pelvic infection. See your doctor for an exam.