I know you're in Nepal, sonypradhan, so understand it may not be easy for you to find a vet who is very good. My only suggestion would be if you can get to a nearby town where there might be a better one. If you can get there, please transport your dog very carefully and gently, just in case there is any spinal injury.
I agree -a vet does need to see your dog. We can't tell you what is wrong.
I'm sorry, but you are asking an impossible-to-answer question. Clearly, your dog is in pain when touched 'in a certain area', and that is due to trauma (an injury) or illness. Either way, he needs a vet to diagnose and treat. You will only find out the cause by taking him to a vet, so do it now.
Tony