A book like, say, It, really can't be described in any other way than horror (and no, I never finished it).

Of course King has lots of books and short stories that are more thriller than horror, and even some that aren't scary at all (such as that short story that was made into Stand By Me). But there are some that definitely are horror.

I've read a fair amount of King a number of years ago, though there's still a bunch of famous ones I haven't read, Carrie among them, so can't really comment on your thoughts otherwise.

Re: the feminine hygiene issue, I'd have to agree with King that in most families, surely girls would know enough to have a clue about menstruation in the 1970s, even if their notions about the details of how to get pregnant or more importantly how not to get pregnant were sometimes a little fuzzy. But of course if the girl is a social outcast and raised by a single nutcase mom, that's a rather different story, and then it's not so weird that she'd be clueless. Though one does wonder if they didn't have sex ed in schools back then...