That is normal behavior! I have been there too, and the best advice I got was to look at the the things I really could be happy about. YOU are raising your kids,You are the rock they they see day in and day out and YOU are the one setting the good example of what it means to be a parent.
I know you have some obstacles right now but YOU can accomplish anything, look how far you have come dealing with the ex...a strong person would not have made it.
I know that the times I feel angry because the ex ruined my credit, forced me to live paycheck to paycheck, borrow money from family....I tried to put a twist on it to make me feel better such as..Well I cannot incur more debt now, I have learned how to budget money much better and I DO have family that love me and wants to help me.
Sometimes the cloud above your head blocks out the blessings that are pouring down. Take a deep breath and think about all the GOOD things that you have.
Peace to you