Can starting a new birth control medication cause a armpit lump?

That should not. be causing a lump in the armpit. An armpit lump can be an enlarged lymph node, a cyst or an inflamed hair follicle (possibly from shaving). Have it checked by your doctor to be sure of the diagnosis and treatment. If it's painful or red, you can apply warm compresses until it can be seen.
No. . No. In general, lumps in the armpit represent cancer or an infection in the region of the armpit. No medication causes this. See a doctor. .