With painful periods w/large clots, the ob gyn did a endometrial biopsy. After 4 days, I'm still spotting/bleeding w/pain after walking little. Ideas?

Unsure. It may be related to the biopsy, or from whatever is causing your heavy bleeding. If you are having fever, you should call your doctor soon. If no fever, some Ibuprofen or tylenol (acetaminophen) if you are not allergic should help.
See your gyn. See your gyn. That's what i would do. Gyn is in a better position to evaluate, and manage this particular issue.