I Have A Throbbing Pain In My Left Arm, What Is It ?

I am 21 years old and am have a throbbing pain in my left arm all the way to my hand! What is it? As of late i have been dealing with a very bad arm pain (left) that at first i believed to be muscle. It has been 5 days now and the pain is still there. I have had slight chest pain and pressure in my chest, but not at the same time as my arm pains. I have been checked for the chest pressure and pains, but two seperate ER s told me that it was non-specific chest pain. I have also had an ekg and a stress test that both confirm a negative for any heart problems. I realize that my age plays a huge role in why i am more then likely not having congestive heart problems, but still i worry about the possibilities. With that said i was also wondering if anyone could tell me the relation between high blood pressure and high cholestrol, if any. Both my blood pressure and cholestrol are well below normal, on a rare exception however my blood pressure does fluctuate to about 159/80 but immedietly goes back to 128/74. Am i right to still believe that my pains are due to some heart trouble hhhhhhhhhhhhh I would also like to add that the chest pains have been around for about 6 to 7 months now. I have been to the ER about 4 times and everytime it has not been my heart that has caused my chest pain. My stress test was a huge negative and I have a regular heart rate, no palpatations or anything. Just the arm pain thing lately