TRICARE PRIME WILL NOT COVER URGENT CARE WITHOUT A REFERRAL.
You need to try and get in touch with the physician on call and tell them you would prefer Urgent Care to the Emergency Room.
I have been to Urgent Care twice this year with my kids (they are Prime). Both times we have had to call our PCM (or the on-call doctor) and explain the situation. Once we got the "blessing" to go to Urgent Care we were given the instruction to call back after being seen with the information of the facility, doctor name, diagnoses, and other random things. Basically, keep your reciept and call back so they can submit a referral into the system.
If Tricare is billed by an Urgent Care facility without the referral in the system they WILL kick it back out and not pay. You will recieve a bill from the Urgent Care. Many Urgent Cares don't take insurance to begin with. In that case, you need to pay up front, get your referral in and then fill out the Tricare paperwork for reimbursement.
Urgent Care and the Emergency Room are different beasts with Tricare. Tricare WILL cover ER visits without a referral. They will NOT cover Urgent Care visits without a referral.