And I mean very grumpy?
DS2 (2.1) is generally not very happy and it breaks my heart that he seems to spend his life in a grump
Occasionally he is happy and will play and giggle but it is not very often - plus he seems to swing from grumpiness to grinning mischievousness with nothing in the middle 
We obviously try and cheer him up, play with him etc but unless he is in the mood, he just pushes you away saying 'no no' all the time. He whinges a lot aswell. I feel sorry for DS1 who loves him and wants to play with him but gets pushed away a lot of the time - eventually DS1 is going to get fed up of trying to interact with him and I wanted them to be close as brothers.
Will he grow out of it? He has always been grumpy, even as a baby, so I fear it is just his personality and I worry about how he will be when he is older.
Any suggestions on how to deal with him to try and make him a happier toddler?