my baby is 13 weeks old. he's pretty manageable in the day time. he takes pretty short naps in the day (typically ranging from 15 mins to 30 mins). of late, he gets really cranky and cries and fusses a lot during the night (aftr 8pm). any reason why?

Could it be that your baby is going through a growth spurt? It usually last for 2-3 days but could also go up to a week. During which your baby will feed more and would need less sleep (hence waking up more frequently at night or taking shorter naps). Other signs would include your baby appearing more restless and clingy. Growth spurts could also cause your baby to have bowel movements at night due to digestive changes. If your baby is indeed going through a growth spurt, you just need to be attentive to our baby’s cues for more milk or attention. And very importantly, take care of yourself. Drink more water and get as much rest as you could. Here’s an article on baby’s growth spurt: http://www.babycentre.co.uk/a25012757/baby-growth-spurts