Generally the ER. Tooth pain is almost always due to an infection (I am not a doctor, etc, etc). The ER will provide an antibiotic that will, in many instances, reduce the pain.

For over the counter visit a pharmacy and get Anbesol, which is a brand name fo ra lidocaine product that is a topical anesthetic that will usually also kill the pain but it can and will wear off after a while. There are generics as well but given the current situation with OTC meds, you may have to go to more than one pharmacy to locate this. I had a family member in such a situation and 2 of us were driving to multiple pharmacies to locate this topics med. We did finally find some.

If you cannot get in to a dentist, consider the dental schools at Boston Medical and at Tufts Medical. You will be seeing a senior student but the teacher will be right there observing and coaching.