Hello,
I cannot confirm anything witout examination but since the rash is in one dermatome,the first possibility is of shingles. Shingles is caused by the reactivation of the chicken pox virus and attack a particular nerve branch in your spine. They always affect only one side of the body (left or right) and never cross the midline. It may thus appear as a band around one side of the chest or abdomen, or down an arm or leg.
The first sign is usually a tingling feeling, itchiness, or stabbing pain on the skin. After a few days, a rash appears as a band or patch of raised dots on the side of the trunk or face. The rash develops into small, fluid-filled blisters which begin to dry out and crust over within several days. When the rash is at its peak, symptoms can range from mild itching to extreme and intense pain.
I would suggest consulting a dermatologist and getting evaluated for shingles.
I hope it helps. Take care and pls do keep me posted on how you are doing or if you have any additional doubts.Kind regards.
Just apply vaseline,if it were some thing like herpes zoster which occurs on one side you would have had pain as the symptom.