I too was in similar position around 15 years ago.
What help/support are you getting from uni? From your support network? Are you accepting all the help available?
Remember if you were working full time you'd be ltd when you could see Ds then too AND you'd be still knackered too!
I treated it as I would have a full time job, but certain things may have changed since which might make this difficult for you I'm not sure.
I had dd in nursery full time (childcare tax credits paid the bulk, it was necessary to have her booked in A's timetable would change each semester) but as I wasn't in lectures/seminars full time I'd take her to nursery same time every day, head into uni whether I had a lecture/seminar or not and if I didn't I either headed to library to get work done or I'd be meeting up with other students to work on group assignments. I'd go to the lectures/seminars through the day then library until I needed to leave to collect dd.
That meant that I rarely needed to do work at home or at least nothing too taxing. I'd email myself drafts/final drafts of assignments to reference and print at home to save money as cheaper to print at home than pay uni costs, even though these were quite cheap.
This meant when I was home with dd I was "present" and focused on her.
Sometimes it was necessary to do some work after she was in bed but that was generally around exam time.
My fellow students were great at being understanding of my circumstances and when it was sometimes necessary to work on group assignments of an evening they'd come to me, but then I'd repay the favour by driving them to mine and feeding them (they were weirdly appreciative of cheap but hopefully tasty home cooked meals)
Uni were good too and supportive both financially and in making allowances with extensions when necessary (not too often but occasionally if dd had been unwell I either had to catch up or was unable to get in to submit assignments, which had to be done in person at that point, not sure if that's still true. We had to show ID and sign a sheet and they had to be submitted as both hard copy and on disk/memory stick)
It's not easy but I'm so glad I did it.
Hope you feel better soon, persevere and good luck with it all.