Chest And Upper Body Pain

Hey guys

Ive been reading alot of these types of forums but recently joined this one. My concern involves my chest area so naturally i had assumed it was my heart. Ive felt pain in my chest area, mainly on my left hand side and towards the middle for a while now. This pain only lasts momentarilly. Ive also been experiencing pain in my muscles such as my back (shoulder blade), arms and neck. This also prompted me to visit this forum as they are 'symptoms' of heart trouble. Anyways ive been to the doctors twice, both said it wasnt heart related. Ive had an EKG (or is it ecg??) and it came back fine and my blood pressure is 120/70. Recently ive also been having pains in my armpit (gland related??) and pains in my diaphram area. Ive began to wonder if this is infact related to the trouble ive been having. I am a 20 year old male who lives a healthy lifestyle, but just for his own piece of mind, would like the opinion of others to help me sleep easier at night. Help is greatly appreciated.