There has been a lump under my right arm for about a year. it fills up with puss. i squeeze it out and about 10 days later, it fills with puss again and has a bad smell. there is no pain though. what should i do?

Hidradenitis: Could be hidradenitis suppurativa. Go here for more: http://www.Mayoclinic.Com/health/hidradenitis-suppurativa/ds00818.... ...Bottom line is that the best treatment is usually surgical removal. You definintely should let a doctor take a look.

Get checked: It depends on where on you arm or if in your armpit. Most likely a clogged follicle or sebaceous cyst which may need to be drained or removed to prevent recurrence. Bad smell usually associated to bacteria invasion. Recommend being seen and evaluated.

Hydradnitis: Most likely you have , infection of sweat glands in the axilla, infection spreads under the skin, usually both sides, needs local care, antibiotics, drainage of infection pockets, if needed excision of the area, speak to your doctor.