I too, had difficulty playing the Inventions -- couldn't even memorize them. Took me something like 50 years to figure out why. Bach had specific lessons in mind when he wrote them, and unless your teacher knows those lessons, you are going to have a hard time. I have written relevant stuff in my book, go to my web page link below, and download 3rd edition and to section (44). With these methods, I gained the confidence that Bach wasn't a problem anymore. Because you will learn so much from geniuses like Bach, you should learn at least a few of the Inventions. They are far, far, better then Czerny, Burgmuller, Cramer-Bulow, etc., that aren't even music and a total waste of time compared to Mozart, Beethoven, Chopin, etc. There are few joys that can compare with talking one-on-one with these giants of geniuses through your music. For your lesson pieces, insist on music you can perform -- why do you think they call piano a "performing art"?? Ever heard of anyone performing a Cramer-Bulow at a concert? Wonder why.