I cannot confirm anything without examination but it sounds like sebaceous cyst. A sebaceous cyst is a closed sac occurring just under the skin which contains a cheesy substance called keratin. They may occur anywhere on body but scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts. Generally no treatment is required but they become painful then it means they are infected, Then surgical excision by traditional wide excision, minimal excision, and punch biopsy excision may be required. Consultation of a dermatologist will be the best in your case.
I hope it helps. Take care and please do keep me posted on how you are doing or in case you have any additional doubts. Kind regards.