I'm roofing my house

Ok so I'm not. But I do have shingles.
It sort of baffels me. Here I am, a pretty healthy 31 year old. I have only been on 1 antibiotic in about 20 years. I don't have cancer (that I'm aware of) I don't have HIV/AIDS (that I'm aware of) I'm not over 60 and frankly I'm not stressed out, so why the hell do I keep getting it?
The other 2 times I feel were explained by the stress that I was under those made at least a little sense to me, but this time ... not so much.
Grrrrr
Well this much is true, I'm a little tired today after getting free food and booze at a baseball game last night and not going to bed till after midnight.
I really need to think about going to bed at a decent time at some point.