Do you journal? Keep track of the things you do that make you feel better and do more of those things.
I have a list of mine on my thread, yours may be very different but whatever these things are, pay attention.
And the up and down is all part of the process, I can remember going from feeling absolutely awful in the morning to great in the afternoon. Don't fight that and question why, just accept and allow and then let it go. We get ourselves in trouble when we obsess about why because that keeps us focused on the feeling.
Say to yourself something like "hmm, I'm feeling really ____ right now but I've felt this way before and it does pass. I know I'll feel better later." and then do something you enjoy.
Me 57/H 58 M36 S 2.5yrs R 12/13
Let me give up the need to know why things happen as they do. I will never know and constant wondering is constant suffering. Caroline Myss