Hi, I have a 2001 Chevy Blazer LT 4.3L V6 4X4 (4 door.) A week ago I noticed that my passenger side low beam headlight doesn't turn on. Day or night, only my driver side works. My brights both work fine. I replaced the bulb, and it still doesn't work. The other day when I got home mid-afternoon I noticed both of my low beam headlights were on, then when I put the truck in park the passenger side light went back out again.
After some fooling around, I found that during the day when I manually turn the light **** right once from the "O" to the middle setting both of my daytime headlights will actually turn on; but when I try to turn on the brights, the brights will click back off instantly.
At night time the light settings **** doesn't do anything at all. In any position it will always keep just the driver side headlight on; except when I turn the truck off but leave the electronics on, then the light **** works properly again aside from the passenger side headlight still being out.

Ever since I got this truck I've been having lots of serious problems that I've had to get fixed. The mechanics that I've had work on my truck have seemed to cause as many problems as they've fixed. Normally I'd pay someone to figure the issue out for me and fix it, but at the moment I'm down on my luck and on a very tight budget so I'll have to fix it myself. At first I thought maybe the problem was a grounding wire, until I got both daytime lights working. Now my common sense tells me that it's probably a sensor or something. Any help would be much appreciated. Could it be a sensor? And is this something I could replace myself?

Thanks, and sorry if this post is a little confusing or hard to understand, I've just been racking my brain trying to figure out how to explain all this.