URGENT CARE is not the emergency room. They do not have the time,equipment, or staff to take care of major problems. Abdominal pain, chest pain, failure of any organ, major breaks, or lacerations need to report DIRECTLY to the EMERGENCY ROOM,. When you are sent from the Urgent care to the ER its for your own health and safety.
Of course the workers are going to be frustrated when you show up 10 minutes before their shift ends when the accident happened 4 hours before that. They want to go home to their families on time just like anyone else. If you have a problem at 11 oclock at night its either to serious for urgent care or nothing that cannot wait till the next day to see your primary care provider. They are not a primary care so they will not treat chronic illness.
Give them some credit I know they do not intentionally do anything to make anyone feel unwanted or unhappy. If you are feeling that way let them know so they can fix the problem.
Have a good day.