Spotting after sex lasting 8 days. expect my period in 3 days. i have 1 sexual partner, have given birth 4 times, this is the first time this happend?

Several reasons: Bleeding after intercourse is never considered normal. Most times it is because of benign conditions, but you can also be a sign of something concerning. I might wait to see if it happens again during your next cycle before you worry. But if it does happen again, then i would get checked out by a gynecologist. They will rule out cervical pathology and maybe do an ultrasound to look for an endometrial polyp.