It took me a long time to really get used to the new routine. I have one child --now going into second grade-- and sort of didn't know what to do with myself once he started kindergarten. (In retrospect, we signed him up for half days for K, which really had me hopping-- I had three hours in the morning to shop, get housework done, get dinner prepped, then go pick him up!)
I found that when I started volunteering at his school, this gave my week a sense of structure and I've continued that throughout his first grade year. Made friends with another mom volunteer who is also a SAHM, which was really wonderful support. Got to meet lots of neat parents as well.
My guess is that once your girl starts going, once you get your school schedule settled you will build your housework schedule around that and your children's needs. It's just getting these layers settled into place that will take some time, some trial and error.
Making the shift can be hard. Honestly, with the half-day kindergarten, it really took me into January of his first grade year to relax into being a SAHM. Likely, we have different reasons for this unsettled feeling. (I was working since I was 16, didn't know what to do with myself at 43 and not working at least even part time. I still sub at a preschool, but not the same.My work ethic/"support yourself" internal messages needed some tweaking to accept that this is okay for right now.) My hope is it won't take nearly so long for you, but my guess is that by the time you are all returning back to school from winter break, you'll feel you've made the transition.
Good luck and please! enjoy your classes! :)