Its definitely TOS related. I'll have something similar- pain for 2-4 days, which goes away for up to a couple weeks before coming back. My pain fluctuates though- it goes from being dull to sharp and then back again, cycling every hour and a half or so. The pain could get much sharper in my left hand, though.

I can't remember the biological explanation for why this happens this happens, but my doctor did mention its a fairly common symptom (if I'm remembering correctly). Maybe somebody else can chime in with some facts that are *actually* useful?