I need advice.

I started a part time job and when I was talking to them about accepting the job I explained that my daughter would be starting therapy soon and would need one day a week off each week. It is in retail so I am scheduled any day of the week and often week every weekend. But I made it clear that this was something I would need time off each week for. It’s the same day every week so there’s never a surprise. I didn’t know what day it was when I started but we had agreed that I would let them know as soon as I found out. A couple weeks in I finally got the call for my daughter to be put on the schedule (there was a wait for it and has been a process). I told them immediately and didn’t have any issues the first week or two as I wasn’t even scheduled for that day of the week. I did notify HR of the day and my manager. I had a verbal conversation and then also submitted it in writing. I submitted it twice in writing as there was a slight change in one of my other days availability but I kept that same day as unavailable. My manager scheduled me for that one day and when we were both at work I approached him about it. I told him how I was scheduled but I wouldn’t make it and I asked if I needed to find coverage and he said it would be great if I did so he wouldn’t have to go changing stuff around. I thought it was a one time occurrence so I found coverage. Since then I have had to do it again twice (I’m only about two to three months in at this job). I told him today I found coverage again and he didn’t seem bothered that I had to do this so frequently but did make a comment about not wanting to get into scheduling stuff which I wasn’t sure what he meant there. Anyway, I go to check my schedule and he’s scheduled me again for the one day I cannot be there. How should I approach this? I can’t keep finding coverage. I feel like an annoyance always asking people and I don’t really have the time between this job, my other job, school, and being a mom. It’s too much and it’s been a constant problem. I’m beginning to think he just doesn’t care.