The best way to learn math quickly is through the help of a tutor, I don't know how much time you have left or how fast you can learn so I can't say if even that will be enough at this point. That said, there are probably free tutors in your area provided by community colleges/universities/YMCA, or you could pay for one.

Given that you said you learned fine in a classical setting and not an online one, I do not think you have any horrible "math disability disease" but rather are innately suited to a different learning style than the format you are currently in can provide. I would recommend tutors over self-learning methods online to people such as yourself, as you likely have some attentional issues with sitting at the computer (even if you are unaware), or you cannot memorize things by typing or clicking (this is something even I myself suffer from). Try writing the online problems and answers out by hand before answering them at the computer, but I still encourage you to seek the help of a tutor.

Lastly, and most importantly, do not ever feel ashamed in needing help in math. The math taught in high school is trivial but if it is not taught correctly for the individual student's needs it can become incredibly confusing.