Don't give cows milk till 1yr of age.. continue breast feeding till 2yrs of age.. give all vegetarian foods( rice+dal and other semisolid foods with ghee/oil added) 5-6 times per day.. non veg, egg and animal products like cows milk after 1yr of age.. Bottle feeding if it is there... It is the culprit.. for this excessive crying.. it has to be stopped and what ever given in that has to be given by cup and spoon.. Look for ear discharge or pain on touching ears.. Head control if attained should be fine.. rolling over you can wait for the present age of 6 months