can't go on like this

I have made a shitty habit of rocking my son to sleep since birth. I spend more than three hours rocking him and he would still cry while I rock him and wakes up every time I put him down. Some nights I have spent over 5 hours. He is now 7 months and am tired of doing this.
I do it for all his naps and take him to bed at 7.30 and can't get out of the room till midnight. He wakes up in the middle of the night to feeed and wants to be rocked back to sleep or else he will just cry. Tried Ferber method at 5 months and didn't work. I'm tired, my back hurts, my arms hurt. Please help I can't go on like this.