I've considered tutoring, but it's fairly expensive, and my (or my tutor's) schedule wouldn't allow me to get as much tutoring as I would need to - given that I sometimes only have time to study during the night.

In my opinion, what you probably need is some mix of tutoring and therapy -- I don't know if it exists, and if there is a word for it -- someone who would guide you through the specific problem, but also through your thought processes, to discover what it is you are doing wrong. Not just what are you doing wrong mathematically, but also what are you doing wrong psychologically. This assumes you would speak your thoughs aloud while solving the problem.

The psychological level is probably more important than the mathematical level, because once the problems with thinking are fixed, you can continue to study maths on your own. But this probably cannot be done without doing the specific mathematical problems, because it's your thought patterns about those math problems that need to be examined and fixed.

I happen to have a background in math and psychology and teaching, so if you would like to try a free Skype lesson or two, send me an e-mail to "viliam AT bur.sk". Don't worry about wasting my time, since it was my idea. (Worst case: we will waste two hours of time and see that it doesn't work this way. Best case: your problem with maths is fixed, I get an interesting professional experience.)