Chronic Staph?

I got my first MRSA infection 3 years ago. Since then i've gotten 18 staph and MRSA infections. I've been treated for them with every antibiotic known to man, including intravenous antibiotics for multiple infections. I have impeccable hygiene, a spectacularly healthy diet, and I don't do barely anything that's bad for the immune system. There has been long enough time spans between infections for me to be pretty sure I'm not giving it to myself (I've moved, bought new clothes, use bleach on everything!) My blood has tested negative for Staph. My white blood cell count is fine. I'm sick of seeing doctors who don't take me seriously (is it cause I'm young and therefore an unlikely candidate for diseases that affect the immune system?) Why is my immune system compromised? I've been a smoker for 8 years, so I know my lungs must not be great. I'm often fatigued (it has nothing to do with antibiotics- I havent been on them in 6 months.) Are there some basic tests I should be getting to see where the real problem is? What Should my doctor look for? HElp!