Do this:

Since all of the nerves pretty much go through the same muscles in the shoulder and back, block your ulnar nerve on the inside of your elbow by applying gentle pressure. If the tingling stops in your pinky, this is a pretty good indication the problem is above the elbow if not in your shoulder.

Another good way to test this is sit at a desk in the typing position; this is easier done sitting at an actual computer. Instead of sitting 90degrees like all of the literature says, lean back a little to where your arms are slightly angled greater than 90. Make sure you're in a comfortable position with your elbows closer to your body. The idea is to limit the shoulder involvement as much as possible. If you notice that the tingling starts to abate, Yahtzee......it's you shoulders. I would single out the traps and levator scapula muscles.

Don't get all crazy like I did, thinking it was TOS. Unless you're doing a ton of overhead work or are an athlete, or have been told you have an extra rib under your collar bone-something that predisposes you to TOS-you probably are misdiagnosing yourself.

Do some gentle stretches for the traps, scapula and chest. If you work at a computer, you need to take breaks, however you can do some gentle spine stretching while sitting at your desk. You should notice in a matter of hours if it's the muscles causing the issue, because all of the tingling will pretty much disappear.

This advice is coming from someone who's been suffering for 2 months now, and only recently did my physio and I figure this out....there was a lot of trial and error. Now I'm back to being a hardcore computer user albeit much more conscious about my muscle tension.

Lastly, you have got to relax. Good luck.