I would start by having your child tested for allergies, celiac disease, and vitamin, mineral, and amino acid deficencies. Pin worms are very very hard to get rid of. I found that keeping vicks on the anal area at night helped to break their cycle along with pyrantel. Take for a week then take a laxitive like magnesium citrate. Do a lot of saline enemas. Wash the linens every day, wear tight underwear, vacuum often and let the sunlight in the bedroom and house. The next week take the pyrantel again and the next morning a laxitive. You want to paralyze them and get them out. they die inside you the eggs move down towards the anus. when they hit air they hatch and reinfect you. They only take 6 hours to hatch. They don't have to be outside to hatch just near the entry. They live in the tiny skin folds. Clean with alcohol the toilets after ever use. Do this for a year. You can let up on the washing of the linens once you get them contained. A clove of garlic inserted in anus keeps them from driving you insane. Garlic inside, vicks outside. Sounds crazy but it works. After you think you've got ridof them treat monthly with pyrantel and laxitive. The cuts on your arm could be strongyloides.