Assuming it has no impurities with greater toxicity and you keep it to once a week and don't keep redosing all weekend, then there shouldn't be severe health effects in terms of your organs or teeth. You say that you're already kind of obsessed with it, so there could me some big emotional ramifications of indulging heavily one day, needing a day to recover, then spending the rest of the week thinking about it. One of these includes the very real potential that you'll give into cravings with more frequent use or take your one day to greater extremes to get the urge "out of your system."
But, yeah, moderate, once-weekly doses of clean meth aren't going to turn your body into shit. The worst of the effects on your body come from heavy use and the lifestyle that goes with it. Some ways to help yourself are to drink water, brush your teeth before bed, dose early in the morning and don't redose so late that you can't get back to sleep at a normal hour, etc. Take cues from those people that keep their shit together while using pharmaceutical amphetamines occasionally. Among the same routes of administration (say, sniffing or oral) you'd be surprised at how similar the street d-meth of current USA and Canada (and others) is to the d-amphetamine in so many ADD pills.
EDIT: I hate to sound like a mom, but I really want to state again the potential emotional consequences you could face. So many people overestimate their ability to control their use. There's also potential for social stigma, guilt, or feeling oneself less welcome or a part of society because of indulging in something that so many people (ignorant or not) do not condone. Think long, think hard and try to be as self-aware and sincere as you can before you make your decision.