My wife and I drive from central Florida to DC every month or so. We stop at every rest area on the way up and back.
So once an hour is pretty good, about the distance between rest areas.
We don't use highways but I would guess that there are large gas stations spaced out just right.
And yes you should see a doctor, just to make sure it's nothing serious.
For the posters that say stay away from Dr's, your chance of dying in an accident in your car/RV are far greater than a death at the hands of a Dr.
Death is always a possibility in every thing we do, it doesn't stop us from enjoying life.