your library may have text books and that kind of stuff for free.
Barnes and Noble sells workbooks and text books / test prep-books. The one near me has a whole section dedicated to it.
There is also a Lakeshore Learning store near me - they are the "Teacher store" kind of store - they are a national chain (I live in USA). They have workbooks, and manipulatives, and anything a teacher could want to buy. It is a bit pricey but I buy a few things at a time for supplementing my kids education. Kind of like extra home schooling on top of regular school.
I had a lot of trouble with math and spelling and stuff in school, so I am always looking for things that help. Some people are just "different learners" - you might be very very smart but learn differently from the way things are taught in school.
What are your strengths? What do you really enjoy doing? you can build on those things.
I like computers and visual tactile learning. I also learn by reading. Numbers get mixed up in my head and so do letters to things like the multiplication tables and spelling I am awful at - but geometry was easy for me and I was good at other higher math. I "cheat" by using high level tricks to make the hard "easy" math work better for me. I know hundreds of tricks.
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ADHD-I(diagnosed) ASD-HF(diagnosed)
RDOS scores - Aspie score 131/200 - neurotypical score 69/200 - very likely Aspie