Well, any of a number of things could be going on. Why do you suspect add/adhd? It could be but you mention things that are read flags for other issues. For example, my son had a terrible time writing. He was resistent to it because it was hard for him . . . he'd have avoided it all together if he could. He had trouble with other fine motor things like scissors as well. He has sensory integration disorder and with sensory which is a processing issue, he had trouble with motor planning. Difficulty with fine motor skills is common with sensory kids. We used the services (still do) of an occupational therapist that worked on this issue and now he'll write and does so just fine. Do you have access to occupational therapists? Some even have writing programs like mini camps in the summer. Our school also employs an occupational service and works with kids that have varying degrees of issues. At the very least a pencil grip is a big help. I'd find fun ways of working on it with him---- here are a couple of examples: get chalk board and a wet cotten ball and chalk. You trace a letter with the cotton ball and he traces it with chalk. Let him erase always (good hand stregnthening). Reverse roles and let him use the cotton ball. Use a dry erase board to do some practice. Tape paper or color pages to the wall and let him color or draw vertically. Have him play with play dough or silly putty. Use pencils cut in half. There is a series of books for English that are excellent called "Handwriting without Tears." Really great. And help him always start at the top and go down (I always said, start at the sky and go down to the ground).
Then when you bring up the issues of his reading, does he have a learning issue such as dyslexia?? This makes reading very difficult. Motor planning with sensory can also come into play with comprehesion.
so can self control, focus, etc.
Our public school system in the US must do evaluations of children upon request and I'd ask for all areas to be assessed at that point. Speech, OT, PT and a psychological evaluation (just to cover it all). Then services are added to help.
You could also seek the help of an occupational therapist and get ideas of where to go from there. OR you can go to a developmental pediatrician. And lastly, ask your child's primary care doctor for where to turn to.
I don't know how the system works in India, but I think you want to get him tested as early and as soon as possible. Talk to his teacher. I am sure the teacher is aware of what is going on. The teacher should be able to help you get him the help he needs.