I'm with Sue T. The beauty of homeschooling is that you can have sick days if you need them and you don't have to worry about it!
I do think you just need some time to adjust. It took me a little while, but I can get them all to the car and to whenever we need to be without too much hassle. Id have to check my old posts on here, but I had a low point early on, but after getting some sleep, I listed out all the "issues" I was having and came up with plans to tackle them all. I also deleted a few things from our schedule/
I also had to start a new morning system with the kids, it works well. I also added extra get out the door time on to it.
It sounds to me like you are tired and need to acknowledge that. get yourself a few good nights sleep, and then spend some quality time cuddling your kids. Don't homeschool one day a week, instead, stay in your PJs and read books, or paint, or do whatever you all want to do.
If your oldest is only in K, you really shouldn't even be worrying about school. Just read to her and play.
Oh yes, if you don't already meditate please get an ap and give it a try. it really helps with the stress!
Edited to add:
In those moments when you feel like you have nothing more to give, remind yourself that you wanted this, remember why, and accept and feel the love. Also remember, it's momentary, it goes by super fast, soon baby will be crawling, laughing, and it will all get calm. I don't know how you do baby sleep stuff, but I did the baby whisperer with my last two kids, and it saved me. I got sleep, I could put baby down for bed in 10 minutes, etc. hang in there. It's momentary!