L.R.
Hmm. Please consider whether your son should be taken to a hospital A&E ward and checked right away for appendicitis, just in case. The fact that the ache is now constant is a red flag the doctor should care about, frankly. Does the doctor know the pain is now constant? Did the doctor actually examine your son or did the doctor just talk to you on the phone?
Symptoms of appendicitis can include vomiting and what feels like "tummy ache" -- you do not necessarily have to have sharp pain in just the right side (the classic symptom) for it to be appendicitis. When my daughter had it, she complained of an ache right "behind the belly button" rather than on the right side. And yes, sometimes appendicitis can linger before the really dangerous, extremely painful stage begins. We thought my daughter had a virus too, until we took her to see the doctor who said, "It probably isn't appendicitis but I want to be certain--take her to the hospital right now for tests." They took out her appendix the next day and she never had the super-intense pain that we associate with appendicitis until about one hour before her operation -- so if someone says, "It can't be that or he'd be doubled up with right-side pain," that's not necessarily true!