6wks ago I developed a lump under my armpit and a few days later they became 2. after a week they disappeared and then appeared again on my right side. They are now 3 and very painful. Is it because I had started using anti-antiperspirant or its some deep

This could be. a simple infection of the hair follicles that coincidentally occurred on both sides, or something more chronically infected known as hidradentitis suppurativa. In either case, it needs evaluation. Your doctor will likely prescribe antibiotics, possibly after a culture is obtained. Depending on the severity of the infection, incision and drainage of the lumps may be necessary. Make an appointment!