the reason im doing a low bar back squat is cause its what is outlined in the starter strength series. Im not saying its the end all be all, but i am a beginner, and as such, feel it was a good place to start.
I was reading in his book the other day and came across a passage. it reads
"Most people have a mental picture of the hands holding up the weight, and this usually ends up being what happens. The bar sits in the grip with the thumbs around the bar, the elbows end up directly below the weight, and nothing really prevents the bar from sliding down the back from this position. People that do this will have sore elbows, a horrible, headache-like soreness in the inside of the elbow that makes them think the injury occurred doing curls."
So the reason i've been trying to keep my elbows "up" and "back" and my thumbs on top is to avoid this. But as someone mentioned above, i do have a shoulder flexibility problem. My wife has commented (read: made fun of) this fact because it causes problems with trying to scratch certain places on my back haha).
Rippetoe says to keep the back of the wrist in line with the forearm when the elbows are raised up. Thus avoiding weight being placed anywhere but the back. I tried more so today (ill post a video) to make sure this was the case, by semi exaggerating my hands being on top. But my shoulders REALLY would not allow it as much as i would've hoped. Anyways, ill post the video. I think what some people here have suggested is congruent with what i have found on other sites. I.E. try front squats etc, ill even look around the area here to see if there is a alternate squat bar available. I love the back squat but it's making it impossible now at this point due to pain to bench or do anything like power cleans after squatting, as the pain is so intense.
(NOTE: in the video ignore the first little bit or so, i was having issue finding a place to put the stupid little camera i used to take the video...)