DD#1 certainly was less than perfect when DD#2 came along. She would have tantrums (which she had never had before), day sleeps went a bit awry but nights were thankfully ok.

It didn't last too long thankfully - maybe 4 to 6 weeks before she was back to her old self. Just try to give your DS some special time with his Mummy (easier said than done with a new baby I know) - bath him if you can while your DH looks after your DD, take him for a walk on his own etc. He is used to having you all to himself and now a new, noisy little interloper has come along and she doesn't appear to be leaving!