Firstly, I'm so sorry for your loss.
Some time ago when I was going through a pretty rough patch I read this... "happiness like other emotions, is not something you obtain, but rather something you inhabit."
I also think that when you aren't feeling "happy", you can strive for that feeling because you feel that you should be feeling that way....especially when surrounded by the well-meaning, the media hype etc.
When I felt like that...I literally just took small steps, not focussing on being happy but just getting through the day. Then i slowly found there would be a tv programme I wanted to watch, a book to read, I'd buy little treats to eat....it's all a road to something better, to being a little more kind to yourself and I can recall the day when I just didn't feel so sad and unhappy any more, I wasn't bursting with happiness, I just felt ok and maybe that's fine too!