It is normal for your cat to behave like this. You can use liquid food like chicken broth or something like that. And if you give your cat wet food then make sure it is totally liquid. And for diarrhea, you can consult with doctor or someone specialist.
I guess your cat is the smart one. That's why he can give you the innocent look. You just need to give your cat a little guidance. And get him toys and increase his physical activities. It will do work for him.
Don't cut the potion of food suddenly. It can cause a bad impact on your cat. He may get sick. You can try some physical activity with your cat. Like moving around. Like the others have said, you can give wet food to your cat. Moreover watch what you are giving to your cat to eat. Make sure your...
Maybe your cat is experiencing pain or discomfort in that area. And that's why it is licking. Try to give your cat full attention because sometimes when your cat is bored or alone, he can try to do this. Or maybe your cat is stressed, or anxious.