I just really don't get why I don't do well in math, which I assume would be the best measure of one's fluid intelligence.

Scholastic math is a different beast. I can say that a lot of professors have issues with the "standard" math curriculum. I have taught university calculus myself and I don't think that the curriculum and textbook I had to work with had much to do with "fluid intelligence".

It seems that my mind lights up with too many questions when I learn math, many of which are difficult to answer. (My professor does not have much time to meet students for consultations and I don't think I want to waste his time). It seems that I need to undergo suspension of disbelief just to do math, which doesn't seem right given that a lot of it has been rigorously proven by loads of people much smarter than me.

Sounds like one source for your troubles. It's a lot harder to succeed at school math and go through the motions if you have unanswered questions about why the method works (and aren't willing to blindly follow formulas). By all means bring your questions up to the professor. If he's teaching, there's probably some university policy that he be available to students for a certain amount of hours outside of class (i.e. it's part of his job). You lose nothing by trying. Even an e-mail wouldn't be a bad idea in the last resort. In my experience, professors tend to complain about students who never seek help until they show up the day before the final at their wits' end (or, worse still, after the final to ask why they failed). By that point it's too late.

Things such as why dividing by zero doesn't work confuses me

We like our multiplication rules to work nicely and division by zero causes problems. There's no consistent way to define something like 0/0 (you could say that since 1 x 0 = 0, 0/0 should be 1, but this argument works for any number). With something like 1/0, you could say "infinity", but does that then mean 0 x infinity = 1? What's 2/0 then?