1st go for hearing evaluation,to rule out hearing issues,after that consult developmental paed or clinical psychologist for detail evaluation Start speech therapy as soon as possible so that child get to his language skills and start communicating.

Children's speech and language development follows a typical pattern. For example at first birth day the normal children speak at least one meaningful word, at the age of 2 years they should able to combined two words and at the age of 3years expected to speak in sentences .The deviation in such pattern is considered as delayed speech and language. Early professional help (Speech language therapy) can be very much effective for developing the communication skills and achieving academic goal among such children. Pl consult Audiologist & Speech Language Pathologist for detail evaluation earliest.

From what you have described,  it seems like your son may have attention deficit hyperactivity disorder.  It cannot be confirmed unless your child is physically examined  by a pediatrician, pediatric neurologist or a developmental pediatrician.