What Causes Sudden Onset Of Stabbing Pain In Left Arm, Shoulder And Chest Area?

hello dear Sir....
am a 27 year old male weighing 180 pounds. my living involves about 4 times exercise per week that includes cardio and weight lifting. sir its been worrying me for two years now. i have sudden pains in my body which render my living realy uncomfy. th pain is like stabbing, squeezing or what i may say itching type that affects my left arm shoulder n chest area . it may start from any where with any intensity and lasts for any longer time as it wants. it renders me helpless and suffocated that i even fear goin anywhere alone with the belief that am heart patient. no tests however hav established that. my aerobic fitness is quite good my resting pulse rate is 55to 60. so as evribody tells me its nerve pain, stress related and disturbed stomach... i need ur expert advice as to what is wrong with me and how can i cure it .... regards: majid