It's been what... 6 weeks, a couple of months?
You need to "cut yourself some slack". You've been through a lot! You need time.
You are still going through the storm, and it's tough. Divorce, custody issues, child support issues, legal wrangling, not to mention the crumbling of a relationship that was a primary focus of your life.
You've got all the responsibility now too (not that you didn't before - we all know how that is) but now it's official. It's a tough wagon to pull by yourself! No wonder you are tired. You have good reasons to be tired.
There were days that I thought I wouldn't get through it. Days I'd start the day with saying "Oh God, please help me to get through this day" before I even set one foot on the floor! Days of feeling overwhelmed like you are feeling. It's stressful. Divorce is stressful and not a quick process. (I don't know how many times I said "it should be harder to get married, and quick and easy to get divorced!")
Take time to enjoy the little things in life. Spend quality moments with your child when you can. Take time to say thanks to your HP. Pray. (it helps!) Get a good nights sleep. If you can't sleep, consult with your doctor for some help. I ask for something to help me sleep - as my mind was racing, worrying about things at night. The days are much easier to get through if you can sleep at night.
Now... this is important to remember: THIS TOO WILL PASS. You WILL survive. Your life will take a new path, a wonderful, peaceful direction. It will come!
I survived. You can too!