Water fasting, or even juice fasting, for more than 24 hours can really stress your adrenals. They won't kill any parasites either, though I guess you are using them for cleansing, though I'm not say they are helpful for that in the long run.
It does sound like pinworms but chances are great you have other parasites as you can start to determine by following links started below.
The info on pinworms may not really be needed, because if you do the general parasite cleansing I suspect they would be killed anyway.
Re the topic of enemas sometimes mentioned in the link above, I am adding a personal feeling of caution about colonics - professionally done high colonic enemas. I have seen them really depleting people's energy, though some really like them. They do flush out a lot of good bacteria & probiotics along with the junk.
There is really no data that I know of to show that good bacteria can be replaced by over the counter supplements, or even things like acidophilus yogurt, kefir etc., after such a highly invasive wash of the intestines. (You can tell if your yogurt or kefir has live probiotics by adding a heaping tbsp. to regular milk, then letting it sit for 8 -16 hours. If itís the real stuff the milk will thicken and give you more yogurt or kefir.) Maybe so, maybe no, but there is new info coming out that low probiotics in the gut can cause things like depression (see Dr. Mercola & Dr. Marsha Campbellís Youtube vid for example) and even possibly things like autism if the mother's probiotics are too low and she doesn't pass enough onto her baby in the birth canal or through her milk.
There are other ways to clean out the intestines, for example some like Blessed Herbs, some like Oxypowder . Simply adding more roughage & drinking more water can be effective.
I'm no expert on any of that, just presenting what I worry may be a potential hazard. Mho.
***HOW TO KILL PINWORMS:
Pinworms are very serious. They can cause appendicitis for example.
You can get rid of them (though if others in the home are carrying them, or you are exposed to their invisible eggs elsewhere, such as in schools with little children then you have to figure out how to not be reinfected) with Noxema or some kind of harmless cream mixed with a good quality (maybe Aura Cacia) eucalyptus essential oil. Mix it so that it feels tingly on your anal orifice but not at all painful.
What you do is keep the mixture liberally on your anal orifice 24/7. If you have a bowel movement, you reapply instantly. Maybe keep a little mini jar, such as you can find in the beauty section of a drug store or grocery store, of it in your pocket. If you are a woman you might want to wear a sanitary pad to keep the mixture from going thru your clothes. Or if you are a man maybe wear 2 sets of undies.
It can take 3 weeks to 3 months to kill them that way. You must check for any sources of reinfection if the problem recurs. The reason this method works is that the pinwroms have to come out to lay eggs. When they meet the eucalyptus oil they will die instead. Also, some people are exposed to family members with pinworms yet donít get them. This seems to indicate that the sufferer may need to strengthen the immune system.
Having said all that, I don't know but strongly suspect Pharmaguard, i.e. food grade diatomaceous earth (see ebay for one source) will kill them too and more simply. I would say use it almost every day for life to tell you the truth. It doesn't just kill pinworms. Mho.