Not Feeling Well

Man, I've been having a lot of these symptoms the last 5 months, when I get on the computer for like 5 minutes I get a headache and dizzy and nauseous, I'm still trying to figure out what it is. I've also been getting a lot of stress and anxiety for no reason, I get dizzy often, lightheaded, my lungs always feel heavy 24/7, its the feeling of having a really bad chest cold. I also have shooting pains on the back of my left arm, but I doubt its a heart attack or anything. I've been real weak, hard to concentrate, It takes me awhile to remember stuff, some nights I'll get 3 hours of sleep, others 12 hours, I've got dark circles under my eyes now, I just feel feel mentally and physically sick. I went to the hospital when I felt like I couldn't breath much, they took 2 X-rays, an EKG (I think thats what its called), listened to me breath and my heart, said they saw nothing. Do you have any of those things? I've been real healthy my entire life, until Jan this year.