Why does my puppy yelp so much?

He is about 12 weeks and ever since we got him he has had a really bad yelping problem. It's like whenever we picked him up weird he would let out this terrible yelp, like he was in pain. We took him to the vet yesterday and got his DHPP, and got him deowrmed. But it seems like after that, the yelping problem has gotten worse. I can't pick him up at all now, or else he yelps and yelps and doesn't quit like he'll be loving on me but he'll yelp so loud and so much. Like he is in bad pain. The vet said he was a normal healthy puppy. Does anyone know the reason he might be so yelpy? He is 12 weeks and a Pomeranian by the way. I have had no problem with barking, he already knows 'enough' means no barking. but the yelping is terrible. Does anyone know how to fix this problem?