4-5 week pregnant yesterday had intercourse and today noticed very light white but brownish white mucus and some cramps, is this because of intercours?

Prostaglandins. The cramping is due to the prostaglandins in semen, which can cause mild smooth muscle contractions. The discharge is light spotting, and as long as it does not get heavier, should stop soon. If anything persists for more than a day or so, go see your OB.