yeah, I've been there....
What I found really helpful was sharing that feeling with others and also having compassion for myself.
Telling myself it's OK to feel sad. It's human to feel these emotions sometimes. Rather than fight them, I'd accept them.... yet also move forward, not dwelling in them.
Take a walk, ride a bike, go to the gym, canoe, read something inspirational, play a guitar, meet a friend for coffee.... continuing to mold my life in the direction of what I'd like it to be - even on the down days - kept me going through those down days.
I don't deny my sadness but I also don't try to fight it or solve it or run from it. Just let it be, while also continuing to work on ME.
Like anger, like the clouds, like happiness and joy and pleasure.... sadness will pass.