How long have you been bottle feeding? Where is the calves mom? DId she get colostrum? I had a calf born years ago, after 2 weeks she was nearly dead. She had suffered before I took her out of the pasture ad was having a very hard time coming back from it. I took her to the vet, where he gave her IV fluids. She was so close to dead, he had to cut a hole in her artery to even get the IV in. She perked up with the fluids...like in 20 minuites. I bottle fed her three times a day, gave her Nuflor for possible pnuemonia.. ended up having to give her meds for coccidiosis, also. She was very weak for a while and I had her in the barn with a heat lamp. She made it.. is 5 years old now and has given me some of the prettiest calves..
I guess my advice would be call the vet...