There is Developmental delay as child is not sitting or not supporting his weight till now. And the child is receiving inadequate nutrition as in this age minimum 3 feeds with solid food(complimentary feeding) can be given to achieve good growth and he is crying with hungry.
And coming to his knee joint swellings scurvy
and other disorders like syphilis
to be ruled out. So present the complaints to Senior Pediatrician
and discuss these issues with him and you will definitely get help.
Dr E Venkata Ramana,