I've been studying math for about 9 months now, not especially intensively, as I studied other things as well and the school stuff and exam anxiety also unexpectedly took a out a huge chunk. I sucked at it from 3rd grade of elementary all the way to college, but after some thought, I figured out about a year ago that it was the math teachers, classmates, grading, and the school bullshit in general that I hated and wished to avoid, not math itself, so I decided that I'll be good at it in spite of school. I used khanacademy and I rebuilt my math skills from the ground up, meaning I really started with addition, just to dust it off. I got to about 4th high school math(logs, goniometric functions, eqs with this stuff,...), but then anxiety from the final and the graduation exams and the bachelor's thesis kicked in an I was out of order for about 2 months. I never encountered it before, I didn't know what to do with it, and it just blocked all my thinking and learning capacities. I looked at stuff, I read it, but I just wouldn't take anything from it. The only way to somehow ease it was to work on the thesis and study for the exams. As soon as I did something else, pressure went up, stomach tightened, and something was pushing me towards studying the stuff I'll be examined on.
When I got back to math after those abovementioned two months, I found out that I just forgot everything. I yet again have no idea what to do with goniometric function in equations or what those things really are. I somehow remember the difinition, but I don't know how and when to use them. The same goes for logarithms. I know which number does what, but give them to me in a equation, and I'm stuck. Things get even worse when I need to actually apply those concepts, such as for using logaithms to get a variable out of the exponent, or even just noticing that I could add the variable to get it to he other side and then factor, or soemthing along those line. It seems to me that I just memorized a bunch of rules and tricks and automated their use to some extent(and forgot a good half of them during the stress period), but that I never actually understood the concepts behind them, meaning that while I can easily solve the problems which are exactly like the examples I saw, I'm lost the socond I see something that asks me to apply the underlying concept, to really understand it. It's as if I memorized a few sentences in a foreign langage to use in certain exact situations, but didn't really understand what the words mean or where else are they used, meaning of course that when the situation changes slightly, my "foreign language" skills are useless.
TLDR version, or just the last paragraph
So, how can I actually learn what math is, what the equations really tell me, what to imagine behind them, how to know intuitively which steps to use to solve them, etc. How do I learn the actual meaning of the language of mathematics? What's the psychology behind this? And is there a course or a book somewhere that teaches you this skill? Besides khan, I also tried the "Indroduction to Mathematical Thinkig" course on coursera, hoping to accomplish this goal, but I lost the latter half of it to the anxiety.