welcome to the hcm forum
form the descrpiton you have given i would like to know more in the details about the pain what aggravated the pain what relives the pain from where the pain starts and what are other symptoms asscoiated with it
how ever since you have said your pulse differs on lifting your arm i would like to have a xray of your cervical spine
ap/lateral view to rule out the cervical rib
cervicla rib is extra rib in few individual which some times may leead to compression of the blood vesselor nerve
which may be the cause of your pain.
if the xray show nothing then mri
to rule out the cervial rib or any brachail plexus neuritis
i would advised you to meet orhopaedician and take furthur managment.
wish you good health