Am I the only person who gets armpit rashes? How do I get rid of it and why do I get them?

I keep getting tiny red bumps in my armpits that only sometimes itch and when they are really bad it hurts to leave my arms at my sides. It might be some sort of a heat rash because I think when leave my arms open they get better. I get a rash like this either severly or just a few red bumps at least once or twice a week. When I dont shave or use deodorant I rarely get them and it seems like they et better when I put lots of lotion on them. Sometimes some of the bumps look like white heads but if I pop them it really hurts and just clear liquid comes out. Im in pain and I wish I knew how to make them go away but I still need to keep shaving and using deodorant. I also wanted to know if other people get this too. and does anyone know why I get them so I can prevent the rash. I feel embared when I wear tanktops and its summer!!