Ouch! Nasty little problem.
If it is indeed parasites, there might be teas that work (for example, you noted the sage tea -- sage is related to
Wormwood ).
It's certainly something to try.
Keep in mind, though, that you might need to consume a lot of it to see any effect. A single, small cup with just a bit of sage steeped for a few seconds probably won't cut it.
You might also be able to find something in the natural foods section of a large grocery store, or at a specialty health food store. There are cleansing formulas (7-day, 21-day, etc.) available at retail outlets. I can't vouch for how good they are. I've used one for colon cleansing and
parasite stuff, but I didn't really notice any parasite-related stuff from it, just the colon cleansing. You might ask a clerk or stock person in that section for assistance, to point out where such items are kept.
Note, however, that most, if not all, such cleansing products state that they are for adults (i.e. 18 and older or 21 and older, depending on their legal department) only. Because you're only 16, you get to decide on your own whether or not you want to violate their recommendations. Tictures that you can find won't usually be labeled in such a way (other than "keep out of reach of children").
It would probably also be hard to find a natural healer of some sort on your own that can accept you for an examination without your parents knowing about it. They might freak out about your situation, but, then again, they might just appreciate that you confided in them about your problem. Parents are strange creatures... (I am one... *grin*)
Good luck!
=-John-=