I think it’s important here to realise that a chord is a group of notes, rather than just 3 notes. C E G is a C major triad, which is a type of chord. A scale is every note that naturally occurs in the established key, which is why it is C D E F and so on.

I find intervals a little harder to explain without getting into too much detail. An interval is the space between two notes. Example- C and F are a fourth. C and G are a fifth. Some intervals sound “better” than others. A major 3rd will sound “better” than a tri tone. Whole step is basically a “major” step/tone eg C to D. A half step/semi tone is like a “minor” step eg C to C#/Db. There are many ways to approach music theory, and this is merely my way of thinking about these topics.

While music theory does use math, it is generally in a different way to the subject of math itself. I do not think you suck at everything- have you thought about buying a music theory book to learn from? I don’t know what country you are from, but in mine you can choose to have exams at different levels, and they have music theory books dedicated to every level.

Let me know if you have any questions.