It definitely could be TOS, but it could also be a number of other things. TOS is primarily a diagnosis of exclusion; similar symptoms can be caused by other nerve and/or musculoskeletal disorders (from things as simple as a pinched nerve to as complex as a brain tumor). You didn't mention it in your post, but have you had any tests (MRI, CT, etc.) for your migraine and pain symptoms over the years?

I feel your frustration. Too often, doctors lean toward treating the symptom ("here, have some Imitrex for the migraine and a muscle relaxant for the arm pain") without finding the cause.