What kind of job do you have? If you have a job where you spend a lot of time behind a computer screen, it could be the cause too. Make sure to set up your seat according to YOUR needs.
Secondly, it could be that your major pectoral muscles are shortened. This may put pressure on your rhomboid muscles, and overstretch them. Try to stretch your pectorals and strengthen your rhomboids.
I have no medical experience, but this is what I currently do since I am having the same issue (although only for a few days now). It helped.
And please do warm up properly. You may feel uncomfortable when other people see you doing is (I rarely see people warming up without using a tennis ball on court), but you aught to. It saves you a lot of misery and pain. Good luck.
Thanks Frenzy. I do sit behind computer screen ALL day. What do you mean by set up your seat? I am using an ergonomic chair. I have a keyboard tray and what else should I be looking into? Please provide your personal experience.