What could cause pain in my temple 3 weeks after my jaw popping out of place?

Muscle strain. Sounds like your temporalis muscle might have been affected. This muscle is used in closing the jaw.
Temporalis muscle. You likely have a residual muscle strain from the episode. The temporalis muscle wraps your head form both sides. Headaches are common when this muscle is in spasm or is strained. Take a nsaid, warm/cold/warm/cold packs 5 mins each will start to resolve the muscle soreness and your headache will get better. If not see a dentist who is knowledgable in TMJ treatment.
Muscle spasm. You describe symptoms of a temporomandibular joint (TMJ) disorder. The pain in the temple may be the parietalis (a muscle) in spasm. This may occur as an attempt by the body to limit movement of the jaw due to joint injury or disorder. See a dentist trained in TMJ diagnosis and treatment.
Muscle pain. Muscle spasm associated with TMJ. See a TMJ expert if symptoms persist. Any dentist can be a TMJ expert with the proper training and experience. Most commonly, oral surgeons, prosthodontists, and orofacial pain specialists. Ask your MD, your dentist and your dental society for referrals.