Yer I was like you. Maths was the bomb when I was a junior. Nothing really phased me. I never studied, and just litened in class. Top'd regardless.
But now it isn't working so well.
i'd blame your teacher for that.
when i started piano, my teacher refused to teach me seperate hands style. so i kinder got the hang of it. (although some may say, it's better to learn one hand and perfect it and the other hand and perfect it and combine to make perfection...etc.etc.blah blah...
That is the biggest bs i have ever heard.
Sight reading is nothing natural. I used to be sheeet.
The trick is to basically sight read LOTS every day. Usually i just sight read like 2 grade 3 books in and hour and the next day half of a grade 4 and etc. i just get all my previous grade pieces...