Why do I experiance this pain?

It has been happening for years, I am 24 years old and I experience excruciating pain in my upper arm(s). This pain has dropped me on my knees twice. It feels as if my arm is dislocated from its original socket and the only way to fix it is by "popping" it back in its right place. Like i have said please if any one can help me i would be so grateful!