My 6 month old cries all the time and nothing I do helps.?

My almost 6 month old cries well screams all the time. I have taken him on walks, held him, played with him, fed him, changed him, put him in his bouncer seat, his jumparoo, and his walker. What else can I do? He is ok for a few minutes, 10 at the most and then starts screaming again. What else can I do? I am about to take him to the doctor again and see what is wrong, but what else is there? I need help, I am so week and tired all the time. My other two kids never did this? HELP