What can I do about a condition that was not properly treated?

Medical malpractice is negligence.  Negligence is the failure to exercise due care (that degree of care that a reasonable medical practitioner in the community would have exercised under the same or similar circumstances to prevent foreseeable harm).
Prior to filing a lawsuit for negligence against Urgent Care and the hospital, it may be possible to settle the case with their insurance carriers.
Your claim filed with those insurance carriers should include your medical bills, medical reports (including the medical report from the gastroenterologist), and documentation of wage loss.
Compensation for the medical bills is straight reimbursement.  The medical reports will document the nature and extent of your illness and treatment which will be used to determine compensation for pain and suffering, which is an amount in addition to the medical bills.  Compensation for wage loss is straight reimbursement.
If the case is settled with the insurance carriers for Urgent Care and the hospital, NO lawsuit is filed.  If you are dissatisfied with the settlement offers, reject them and file a lawsuit for negligence against Urgent Care and the hospital.  If the case has settled with one, but not both insurance carriers, only name the party (Urgent Care or hospital) with whom the case has NOT settled as a defendant in your lawsuit.   If the case has NOT settled with either party, name both as defendants in your lawsuit for negligence.
If the case is NOT settled, your lawsuit for negligence must be filed prior to the expiration of the applicable statute of limitations or you will lose your rights forever in the matter.

You *may* have a lawsuit; the issue is whether, under the circumstances (e.g. based on the symptoms you were reporting, what could be perceived about your condition, how urgent the situation seemed to be, and the tests or imaging that were or should have been run) it was reasonable to think that you had gallstones or not. Medical care providers are liable when they are negligent, or careless or unprofessional; but if they gave you professional care and were not careless, they are not liable even if they turned out to be wrong (the law accepts that the practice of medicine is not perfect).
Also, another issue is whether a suit would be economically worthwhile: you can only recover an amount of money related to the medical costs caused by the malpractice, any lost wages, and if you suffer long-lasting or permanent disabilty or life impairment, some amount of "pain and suffering." There are times that malpractice was committed but there's not enough money involved to make a suit worthwhile.
You should consult in person with a medical malpractice attorney, who can listen to all the facts in detail, review any medical records you have, and guide you as to whether you have a viable lawsuit or not. Many such attorneys will provide a free initial consultation, and you can inquire into this before setting the appointment.