Stopped taking 875mg amox for tooth infection because caused severe headaches-3 days later still getting headaches-is this normal?

Not normal: Headaches are not an anticipated side effect of amoxicillin, so i would look for other causes. Either the tooth related infection or possibly something else. Check with your prescribing dentist, or your physician.

Mx reaction?: Personally, i doubt the headaches are related to the amoxicillin, especially since they continued after you stopped taking them. Further, if you have a tooth infection, this needs to be treated and you should still be on antibiotic coverage. I strongly recommend that you have your dentist consider switching medication and address the infection asap. You may need to see md for headaches.