Lump under armpit i think deeper under the skin, not moveable , size of two or three peas, sometimes it grows bigger then smaller, sometimes sore. its been there for almost a year. is this a cyst or what?

It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. You could watch and wait: You may feel the "lump" every couple of weeks, if any of the lesions doubles in size, becomes painful, ulcerates, or other lumps appear, or you develop fever, or lose weight, you should see a doctor. Wish you good health