Aren't you giving any solid food to baby yet?  Try to give fruits and vegetables along with a normal diet. Reduce milk intake. Avoid cows milk as far as possible. Keep breastfeeding but not too much during day time. Try to give Dalia, khichdi, cheela, Dal rice, etc. Try to give fruits like pear,  papaya, peaches. They will help in constipation. If persistent consult a pediatrician near you. Using AC is no problem as long as the temperature of room is not too low and you take baby out in fresh air atleast for few hours a day in early morning and night.  Also try to have some fresh air in room in early morning and late night.