Pain in middle of back and chest wont go away

Hello! It is 12/30/2010 now. I`ve had this pain start the night of the 17th. I was visiting a friend of mine on the 17th and I was leaving her house and I picked her up and gave her a hug. I`m a pretty strong guy. back and arms are pretty solid and never been hurt be picking any heavy things up. but everything was normal till I went to sleep. when I was laying down I had this pain in the middle of my back and chest. it felt like gas.. so I went to sleep and woke up and it was gone. all day it was fine till late afternoon it came back. and it has been constant every since..  my back feels like I have been walking for 8+ hours at a mall... just really dull pain like my posture is off... my chest area feels like gas pains. I`ve taking gas-x.. and some baking soda in water to relieve some gas but it just doesn't help.. eating different foods or laying in certain positions or anything doesn't change the pain whatsoever. after 4 days of this straight I was worried it could be something serious so I went to the ER (avoided it like the plague since I dont currently have a job). did a EKG, xray of my chest and back, blood taken.. everything came back great. and while I was in there my pain was pretty low which was really werid.. so the doctor came in and said well I didnt find anything... gave me a prescription for naproxen and said good day.. and I have been taking some tylenol before I went to the ER and also domsom back pain pills. which didn't help at all. but I picked up some aleve (naproxen) and its been helping great once it kicks in.. pain is almost gone completely for a good portion of the day.

whew.. alot of typing... hehe. I`ve been trying to read all over with SOME help with what this could be. I`ve read alot of stress can cause some pain like this and I have been under ALOT of stress looking for work and worried about bills. but Im not sure this is the problem only since it seemed to start after I picked my friend up..  so because of this I was thinking perhaps it was a pulled muscle, or perhaps even torn some of my core muscles. but moving around doesn't make the pain better or worse. so I have just been taking aleve, putting icey hot on my back, and taking hot baths to warm the muscles up and it does help for a short time.

If anyone would be so kind to have ANY insight on this. it would be greatly appreciated!

- Justin