I have been having severe leg pain for the past 3 days. What do I do?

Be seen. There are a lot of potential causes. You would need to be seen and examined for an accurate diagnosis.
Dont ignore it. how do you know you don't have a clot in your leg which is life threatning? since you don't describe where in the leg, I don't want to scare you - but obviously something is wrong and you should get checked out...
Talk to a doctor. Keep a log book & use HealthTap Prime or make an appointment with your primary physician to discuss the symptoms. Unfortunately, in this forum, we're restricted to 400 characters so we can't make a diagnosis here. Severe leg pain can be due to neurologic, vascular, musculoskeletal, inflammatory, electrolyte & infectious causes. The pain is different for each (burning, throbbing, electric, crampy)
Any other symptoms? If there is no swelling and it could be a pulled muscle or cramp then stretching and massages might help. If there is swelling or no reason for the pain to be present then I think an in person exam would be a good idea. .