How can you tell if you have allergies, cold or tmj? clear runny nose, pain above eye, mild headache, jaw clicking. how to relieve symptoms?

Unlikely one issue: Sinus/facial discomfort would be common to all three. Otherwise, you'd have to have more than one of the proposed causes. TMJ technically refers to the actual jaw joint, which can become inflamed and spawn localized or referred pain and clicking, but unlikely clear runny nose. You didn't mention migraine variant, which could possibly be triggered by TMJ. Get checked out.

More than 1 thing: Might be more than one thing. The jaw clicking is displacement of your TMJ disk. All the other symptoms could be explained by TMJ except runny nose. I'd start with MD, if negative see TMJ specialist.