<< I learned what I know now because of a hunger for solving the "puzzle" aspect of it all. Now, for some reason, it just seems like work. >>
That's why you should learn PHP. HTML design does get boring after a while but PHP is lots of fun and when you're writing scripts it does give you that puzzle aspect when you have to figure out the logical statements. It gets even more fun when you start using PHP as a database interface.
BTW, I never learned any programming in school but learned just by buying one or two books, visiting tutorial and reference sites, and then tearing apart web pages and scripts.