i think I need a second bout
Most of these, you kill off the adults with whatever stuff you take to get rid of them, but the eggs in your system are still around. An *essential* part of treatment is to hit them with a second dose after the eggs have hatched but before the critters get to reproduce. For most of them, I think that's two weeks.
OTOH, I also remember the NewScientist article a little while back where people with IBS were deliberately given parasitic worms that live in pigs. The worms couldn't survive long-term in humans, but did for a bit. Most of these people, their IBS cleared up. A major current hypothesis is that IBS and other similar grief is caused by a lack of internal parasites, so your body's defence mechanisms get over-sensitive with nothing to do.