Feeling sick all the time, what could it be?

I have been to the doctor who did an MRI on my brain and all was fine. My body is achy, my stomach is hurting especially on the sides, my back hurts, I get weakness and tingling in my arms and legs (thats why they did the MRI), fatigue, and dizziness. I just want to feel better and since the doctors don't even know what this is I thought I would see what you guys think. Maybe someone on here had similar symptoms. thanks in advance.