Foot swollen, painful for 4 weeks, x-rays negative

My left foot became swollen and painful 4 weeks ago.
I have no knowledge of injury. Extending the toes causes pain and a tight feeling from the ankle to the big toe, and there is pain across the area on top of the foot, right before the toes. X-rays were negative, and since I am nursing and can’t take anti-inflammatory meds, my physician had no other useful suggestions. The foot has been slowly improving, but the foot swells each day, and I still cannot wear a closed shoe. Could you please tell me what this might be?