That could be a muscle strain... Do you do anything that requires a lot of arm work?? Do you do any major sports??? You could either call or go to your doctor and ask if the feeling is getting stronger.... My advice to you is that you can just take 4 minutes out of your day and pull you left arm across your other arm's shoulder until you feel a stretch. You can hold it for about 1-2 minutes. Then take a break for about a minute or so.. Then do it one more time.. Do a couple times a day... Not to much or else it might make it worse.. See if that helps!!!!