My baby is 5mo and lately he has getting up at night (after a month of getting into a napping routine). He just plays and then sleeps after a good 3-4 hours. What should I do?

Kids these young take time to establish a routine. They eat, sleep, play as per their wish. If you try to stop him from sleeping when he wants to he will become cranky. Motherhood is not easy dear! Don't worry..few months down the line everything will be streamlined.