My 6 month old boy can’t roll over fully. Whenever he tries to roll his one arm got stuck below stomach and he is not able to pull it out. Once I help him to bring that out with both arms he tries to hold his head up. But he hold the head for few second only and then lay down on his tummy and again hold his head up after few seconds. Constantly he can’t hold his head up. He doesn’t like tummy time much… he is so active apart from lying on tummy. How can I improve his tummy activities and could it cause a delay in his sitting and crawling?