We have all had trouble with cattle from time to time.
First I"m going to say you may have been feeding him a little much. But also if you over feed him he would be grinding his teeth and have Sours. So I not so sure.
Is his BM dark or creamy in color?
Is there stool on his trail?
Is he grinding his teeth?
Sound like to me he ate something he should not have.
On and other note I had one one time had to force feed a little bull for 4-6 weeks, one day he just started to suck again. I was a young 14-16 and had the summer off. Used an old pop bottle to force it down the side of his mouth.
A few things to remember about baby cows.
Better to be hungry then over feed. Have to keep them dry. They suck on everything. They can get depressed, and not eat, weather from environment (something they ate) or there own body (not getting colostrum from there mother, or something else). Make sure the head is up when feeding, make the milk go into the gut the right way, plus keeps it out of the lungs. I would wait for a calf to be a month old before try to get them to drink and not suck. They make allot of saliva when they suck, it helps them digest the milk.
Hope it works out !!