Single & pregnant again

I was in a relationship with my ex for 7 years when we had our first child. I ended up pregnant again when he turned 5 months old. I miscarried and my SO and I broke up about a week later. It has been very messy and we have only started being able to talk without fighting this past week. I found another house to rent and just started working again and signed up to go back to school. I've been highly motivated and aside from missing him a bit I've just accepted that we don't need to be together right now. We've talked about possibly getting back together in the future but neither of us wants that right now. Well right after I had stopped bleeding from my miscarriage (we had been broken up for a few days) we had sex. I just took a digital test today and it showed I am pregnant. I haven't even had my first period since my miscarriage.
I am terrified. Now I'm not just a single mom to one child, I'll be a single mom to two children if this pregnancy sticks. Family is willing to watch my son while I work and go to school, but I doubt they'll watch a toddler AND and infant. I want to go to school so I can do better for my family but I'm scared I won't be able to do it now. There are just so many fears. My knee jerk reaction is to try to get back with the father but he doesn't seem interested in that and I honestly don't want to at the moment. I don't want us to be together just because I'm pregnant. I do love him but he's done some crappy stuff and I don't think I'm ready to jump back in a relationship with him. I just don't know what to do....
***Its not leftover hcg. I was negative at my doctor a week after and had a negative test 2 days ago. It just came up positive this morning.