Urgent cares are for the most minor of issues. Urgent cares do not have the sophisticated diagnostic tools such as labs and imaging that an emergency center has. Urgent cares many times are staffed by nurse practitioners, so you don’t see a physician. Emergency rooms doctors are all board-certified doctors, so their medical knowledge and training is much more extensive than urgent care staff. Even relatively minor issues can be leading up to something more serious, and these subtle differences are much more likely to be picked up by a board-certified ER doctor. Emergency rooms basically see and treat the same issues as urgent care except vaccines and wellness checks but also can see much more and give a higher level of care. 

If you can’t wait to see a primary care doctor and must be seen immediately, then your condition is very possibly considered a medical emergency, and according to Texas law, all insurance companies must cover medical emergencies at in-network rates.