C section 14 weeks ago. Since then have had a red, itchy rash in a band around lower back. Is small red bumpy spots, itches on and off. What is it?

Infection? To know for sure what it is, you would need to see a Dermatologist. A common cause of your symptoms is a yeast infection or bacterial infection in the skin. These can usually be treated with non-prescription antifungal or antibacterial skin creams. Best wishes!