cranky toddler

All of a sudden my 20 month old has become a clingy, cranky toddler who always wants to be picked up. We had a similar issue at around 18 months but that stopped and this time around I find its worse. In the mornings now he will push his dad away and only want me, and the slightest thing will upset him. There have been a couple of changes of late; dad just started a new job and now he usually drops him off at day care in the morning.
I wonder if his second molars are coming, as he gets clingy when he isn't well. But there aren't too many other things that point to that. Any ideas?