Why do I suck at electronics so much?
If your profile age is correct, then don't worry. You probably already have an advantage over the rest of the people your age who like this kind of stuff. 

To understand electronics well, it takes theory and also, experience. Both of which you lack. That's not your fault and and there probably isn't much you can do about that yet. But give it time, and go to university so that you can begin to learn the theory. You can't really knoe all the theory now because the math is above your level. As much as you want to say that you can understand the math, you won't.

For what you can do now, stick to what you are doing. Small circuits here and there, and 'tweak' them as you feel fit. Try and understand why the 'tweak' worked and maybe this site can help you for somethings. But when you start going into amplifiers (small signal stuff), it can be confusing and the math behind it is really just algebra(not hard but can be confusing) and that's where a good sense of intuition would come in to help leviate some of the confusing math and the different modelling methods to figure out input and output impedance etc.

You are still young and have much to learn and time is the only thing that can help you understand. 

Keep tinkerin, keep failing, and keep trying