Calves don't get "homesick." They only get sick if they are under stress, contracting bacteria causing shipping fever or pneumonia. Stress always occurs when they are being weaned. A sick calf is lethargic, listless, laying down by himself when he should be up and eating, has goopy runny discharge from his nostrils, dull look in his eyes, and he may cough too.
Constipation. Get a veterinarian out ASAP.
It's possible they have a respiratory illness. Consult your veterinarian about this.
This is a question for a veterinarian. There are many drugs available.
Check with a veterinarian. It could be joint ill or an abscess that needs to be treated.
It is highly recommended to get in contact with a veterinarian about this immediately otherwise you may soon have a dead calf on your hands.
Between 2 to 6 weeks.
The two differential diagnoses that come to mind are calf diptheria or chronic pneumonia. However, your veterinarian will have to take a look at the calf to see what may be going on.
Get the veterinarian out immediately. The rectal prolapse in your bull calf could merely be a symptom of something more serious that needs to be addressed right away.
A stray calf is a calf that has wandered off away from his mother, and/or has been separated from his mother by either the herd moving to another pasture, or by them being sorted, or simply by the fact that that little calf went exploring a little farther than he should have.
Disease or a blockage in the gut will cause a calf to stop eating. This is something you need to take up with your local large animal veterinarian immediately if you wish to have a hope of saving the calf.
That is something you need to talk to your veterinarian about, as I have no idea about the age, sex, breed, other symptoms or any other history of this calf to help you out. Depending on the severity of the sort of disease or illness a calf is inflicted with or whether blindness is a genetic condition, a calf could be permanently blind even if you try to find some way to help it out. So you would be best to go talk to a veterinarian instead of finding any answers on this site.
Look for how much the calf has filled out in its frame, body to leg-height ratio, and weight gain. You can also look at a calf's teeth to tell its age.