I have hidradenitis suppurativa under my arm. is there anything i can use that can help with the itching?

You need to see a doctor as it may require prescription antibiotics. For information on this topic, visit this site: https://www.niams.nih.gov/health-topics/hidradenitis-suppurativa-hs/basics/symptoms-causes

Hidradenitis if persistent needs specific therapy other than antibiotics. A dermatologist can help you with assuring the diagnosis and prescribing treatment