You will have light moments and moments when you laugh and then you know that you still have it in you to be back to happy and normal. It is just a matter of time, and you need to be patient with your blahs.
It's hard to explain what NOT wanting to do anything feels like or what feeling like you CAN"T do anything feels like. Just know that it's ok to feel that way.
Listen
to this many many times, it will help. Mantras have strong healing power and George Harrison did great on this one.