I am constantly getting big pimples under my arms in what looks like clusters and varying sizes.. what can i do to get rid of them & what causes them?

Folliculitis : Clusters of pimple like lesions in the axilla (or armpit area )are usually infected hair follicles. A common cause is bacteria introduced when shaving. It is important that a clean new razor blade be used every time you shave and the area is clean as well before you shave. In addition applying an OTC antibiotic to the shaved area right after shaving often prevents Folliculitis from occurring.