Living day to day

Why are some days easier than others? Why do we have days when we just want to curl up in a ball and cry? My life as a whole right now is very bi-polar. I have a good day and then 3 bad ones. Or sometimes I just have a really bad week. I'm just ready to get to a place in my life when I can have a new normal day with no problems. I'm hoping days like that will be coming soon.