M.K.
I would stop nursing him in bed. Do you have a chair or rocking chair nearby. I know you are tired but nursing in the chair would be better. He is probably used to being near you and now is using you and your body for warmth and comfort. Not at all a bad thing if you are into co-sleeping but it sounds like you are not. After you put him back in the crib if he wakes up screaming then pat him and talk softly, tell him it's ok and let him try to comfort himself. If he just fusses wait a couple of minutes to see if he can put himself back to sleep. Depending on his size and weight he might not be ready to go the whole night without feeding. My daughter was 8 or 9 months before I weaned her of night feedings. I tried the cry it out method and it did not work for us. My daughter would get so upset that she would projectile vomit all over the crib and room plus it broke my heart. For me this is not a way for a child to figure out how to soothe themselves. Find a method that works for you and stick with it. Children thrive on schedules and if you are firm in your methods it will work out.