I have a few skin sores on my left shoulder and near my armpit. what could they be from?

Maybe infection?: Sores in armpit and shoulder could be a minor infection but without seeing it there is now way to be sure. Shaving arm hair sometimes can be the inciting reason and is a common cause of impetigo.( a skin infection caused by staph or strep. I would visit with your doctor. In the mean time scrub the sores well with soap and water. Keep it clean and dry.