there could be many reasons why he cries.
One possible reason could be that he has colic. Try burping him after every feed. then allow him to be reclined for 10 min before putting him to lie on his back. Are you breastfeeding or giving fm? If breastfeeding, you may want to reduce taking food that can cause colic like beans, chocolate, cow's milk etc
Another possible reason is growth spurt. The magic numbers are 3, 6, 9. So, week 3, 6, 9, mth 3, 6, 9 are usually the growth spurt periods where they feed more. So, if he seems hungry, feed him more milk but be careful is not colic else feeding more milk will worsen the situation
sometimes also the temperment of the child. Mayb he just want to be cuddled so just cry.