Alright I've never run into this before but lately my les paul has been playing more or less fine on the rhythm pickup but whenever i switch to the mid or neck it is either completely muted or i barely hear it come through. Occasionally if I switch back and forth enough it'll be the opposite and the mid pickup will work but then the bridge wont. I'm guessing this is a wiring problem and there are no guitar techs in my immediate area; I was wondering if it's common and can be easily fixed or if I should seek out professional help, thanks.
Current Rig:
Les Paul Studio Ash
Martin DCX1E Acoustic
50 Watt Valvetronix
Boss ME-50
Yeah, you can fix it yourself. You need a soldering iron, ($10 dollars at Radioshack) and some knowledge of using one. (Basically a quick online-tutorial)

Get a wiring diagram from google or someplace. Usually Google image search has wiring diagrams, at least they do for Fender guitars. Then just follow that.

*Before you start though, if the problem is consistent throughout the guitar, check to see if your pot is dirty. If your guitar is over 4 years old, this seems to be a common problem. If it is full of dust/wood residue, just wipe it out or use a air spray can.
try adjusting the pickup height or move the pickup around. the exact same thing happened a while ago on my SG. i did that and it worked fine afterwards
normally either the pots or the selector switch. clean them or have a tech do it.
Try junkies idea first. My LP did the same thing. I sprayed contact cleaner into switch and problem fixed.
I'm having a similar problem with my Epiphone Dot Deluxe. I got new Seymour Duncans in it recently, and they sometimes didn't work. It did the same thing before, too, so it's not the pickups. I just took it in yesterday to get checked out. I hope they finish it soon, I'm playing King of the Blues on Tuesday and I need practice.
"Notes are expensive. . .use them wisely"-B.B. King

"It's been very important throughout my career that I've met all the guys I've copied, because at each stage they've said, 'Don't play like me, play like you."-Eric Clapton