This certainly sounds bothersome! As you can imagine it is quite difficult to diagnose a rash or skin lesion without being able to see it and I am glad you have an appointment with your primary care physician
to have a more thorough assessment. That being said, there are a few potential diagnoses that come to mind based on your description:
1) Contact dermatitis: is it possible that you only have these bumps when you wear certain clothing, or a certain belt that may rub on your abdomen in that particular area? If so, this may be a contact dermititis, which is a skin allergy to some material or chemical that your skin is coming in contact with. If the bumps are itchy or irritating, that would go along with this diagnosis.
2) Heat rash (medical term 'miliaria rubra'): although atypical, it could be that this particular area of your body is predisposed to heat rash, which is a follicular rash caused by obstructed sweat glands. If possible, try to keep the area cool and dry and see if your symptoms improve.
3) Scabies: this is less likely, but potentially your rash could be caused by a scabies infestation. Normally this would be intensely itchy and would have a linear pattern.
I hope you find this helpful. As you prepare for your upcoming appointment, taking pictures of the rash at different stages and bringing these photos in to your office visit may be helpful for your primary care doctor