Why do i feel that i'm not smart anymore.

No one here is qualified to answer this question.

Get counseling or see a medical professional. Could be the starting of depression. Could be something like the beginning of ADHD.

More self-confidence

Mathimatics reaches a point where even college professors will have to stop and think. Their is no math master. Math is like Chess, you could only get better with practice. You have to keep on practicing it even into your old age. As I went up the ladder in my college many professors started to slow-down.

Between

Trigonometry + Algebra + intro to computer science ( and my dad who did telecommunications) all of them talked about the subject of wave oscillation ( forget other term ).

I will admit what you just said, I was like you. Was in hospital for pneumonia. Stop studying. Went back and had to study because I was lost.

Your on the right path. You said #@$@$ what was in front of you and go your own way.

Elementary Mathematics = K-12
Trigonometry and Algebra = College basic requirements for most majors
Computer math = Decimal, True False Tables, Binary, ANSI, Hexadecimal
Physics = Applying mathimatics to real world problems
Astro Physics = like above but dealing with rocket-fuel like NASA and Space-X, or even the projector ( like how to travel to the moon using the gravity range without using so much fuel ). Even how the shape of something is designed.

Here is the problem your in school still and know you can do more but while your in school study what the teacher requires you to study. Get books and study them without your teacher. Go to math-camp, Using online math programs and math-meet-ups and free help online. Higher a tutor or even do a group-on for tutoring.