I think I have a staph infection again?

Okay so I got a staph infection on my leg last summer and I went to the doctor and went on medication and it went away. Then I got another one last fall during my volleyball season and I did the same thing and again it went away (it was on my arm pit, weird I know..). Now I have two little bumps on my other arm pit...they hurt like a ***** too, just like the other ones. I think i'm going to the doctor today but why do I keep getting staph??? I know my immune system is really really weak, could that be that cause?