threadworms don't normally itch during the day but do quite intensively at night. Sometimes, you can see them crawling out in the late evening - you could get dh to have a look or try and bend over in front of the mirror when it's very itchy at night. They look like tiny threads of cotton.
If you are really infested, you might be able to see them in a poo but I do think it sounds more like piles.
If it is worms, you don't necessarily need a treatment - theoretically, they have a 6 week cycle (think it's 6 weeks). They come out and lay eggs around the anus, you scratch and then ingest them and they are reborn. If you don't ingest the eggs, the cycle stops. Problem is the eggs get everywhere - bed linen, in the dust etc. so if you think it is threadworms, wear knickers in bed and wash your bum every morning.