I wasn't at home from morning to evening. Morning I had given the cat some milk and left for college. When I returned in the evening, I notice that the kitten is trying to "meow" but it isn't able to make sound. It's trying hard but either the voice itself isn't coming out or just a very low volumed "meow" is coming out of is mouth. Before this it used to have a loud and sweet "meow". I am very much worried as to what has happened. please say what to do.
If the cat isn't meowing normally again in 24 hours, I'd go to the vet. It might be a furball; a cat trying to pass a furball can look like it's trying to meow. But the fact that it is making a soft meow rather than a weird yowl or no sound at all seems strange. Stress or depression can make a cat stop meowing altogether, but I wouldn't expect a soft meow in that case. Possibly it has a bit of string caught in its throat, or it swallowed something it shouldn't have.
Most cats don't digest cow milk properly. Goat's milk is a good alternative. There are also commercially available "cat milk" products.