Summarize the following:
If the bumps under your arm are sore, itch, or bleed, you should talk with your doctor immediately. In some instances these pimple-like bumps can actually be cysts or in severe cases a type of skin cancer. Ask your doctor about the pimples to see if they are something more serious. If your doctor identifies the red-bump as a cyst, they may elect to drain the cyst. It is important that you do not attempt to pop the cyst on your own. This can actually spread bacteria and may lead to infection. Have your doctor or dermatologist drain the cyst using a scalpel or needle.  This will not remove the cyst, but can reduce the swelling if the cyst is pus-filled. If you get cysts repeatedly, your doctor may prescribe you a low-dose antibiotic. In some cases your doctor or dermatologist may recommend removing the cyst. This is typically done if the cyst is large and is accompanied by painful symptoms. Cysts can be removed surgically or through laser treatment, depending on the specific case.

Summary:
Ask your doctor about the pimples. Have the cyst drained. Get the cyst removed.