102.5 fever in 2 1/2 year old. Should I be concerned enough to take to urgent care our treat at home? He said his stomach hurts. But no other symptoms

Should be seen today. With a fever and stomach pain, and no other symptoms (no cough, runny nose, diarrhea), we worry about urgent things like appendicitis. I would have him seen today especially if he's vomiting. The doctor should do a good exam of his belly, will also take a urine sample to look for a bladder or kidney infection. Good luck, and hope he feels better soon!
Role of fever. The fact that your son has a fever means that he is sick with something. Unfortunately, it does not tell you if it is due to a virus (no treatment other than supportive care) or a bacteria (may need an antibiotic). With few symptoms, it should be ok to give him some Acetaminophen or Ibuprofen for the fever overnight and have him see his doctor tomorrow. Urgent care is ok if he worsens.