Some quick points here:-
"I knew that if you have lots of zits, the gothic look can look painfully stupid"
- only if you mean heavy-handed lumpy foundation over a less-than-flawless skin. This not only LOOKS bad, but can make your skin even WORSE if you're using certain cheap "gothic brand" white foundations, as they're mainly not great quality, and oil-based.
Foundation wise, look for something that's oil-free and non-comogenic (non pore-clogging). And consider the advice that others have already given: heavy white white white foundations are kinda out in the goth scene ANYWAY at the moment, and really aren't flattering - if you want a ghostly pallor, try white powder on top of more "normal" foundation.
Another tip I'd give for doing the goth look if you have pimples, is to avoid wearing red-toned makeup (lipstick or eyemakeup) near any "problem" area as it will bring attention to the redness of the pimples: I think blood reds are great on lips for a gothic look, but try wearing something else, like a darkened plum or a metallic shade, if you 've zits near the mouth area.
And once more as other folk have said, another great tip is to use dramatic gothic makeup to draw attention AWAY from the worst bits of your face: if your chin is spottiest, wear REALLY dark eyemakeup and lots of smudgy liner... if you've blemishes on your forehead that you want to hide, but your chin and cheeks are clear, try a really dramatic gothic lip instead.
Good luck, and my sympathies with your skin troubles. I'm in my thirties and still suffer from oily skin, but remember well the skin of my teens and it was HELLISH, so I know where you're coming from babe! Just persevere with decent skincare (though AGAIN as others have said, be gentler on your face! Don't wash too much!!!) and remember to try drinking as much water as you can: it's a great way to balance out an oily skin, and is the cheapest skincare tip around!
Finally: remember that an oily skin now = FAR less wrinkles and much glowier, younger looking skin when you get a bit older, you will age better than other girls your age! I know that doesn't help much right now, but you'll get to be beautifully smug later on I promise!!!!