Probably should go see the doc. It might be herpes.
Normally welts appear in a skin condition called hives.Hives are red, itchy welts or swellings on the skin that often come in clusters. Hives can appear anywhere on the body, cropping up either in one small area or covering large patches of skin. They most often occur as part of an allergic reaction. No one lesion lasts more than 24 hours, but new ones may continue to appear until the condition resolves.
Hives associated with pain are seen in a few auto-immune conditions like Rheumatoid arthritis.
In your case, it may be herpes but the lesions are usually fluid-filled blisters.Can you give us some more information as to how long have you been having the problem?Do the welts itch?Do you take any meds for the pain?
It will require an examination and some follw-up to come to the correct diagnosis.