Why does my bottom itch?

I have started getting a very itchy bottom, particularly around my anus. The itchiness is worse at night and it’s very sore when I go to the toilet. I’m too embarrassed to ask my doctor about it, can you help?
I’m afraid top of my list of possible diagnoses would be that you have worms. The adult worms lay their eggs on the skin around the anus at night causing itching and as revolting as it sounds you are then probably passing eggs from under your fingernails into your mouth. You can break the cycle by bathing every morning paying particular attention to your anal area and being fastidious about hand washing and nail scrubbing before handling food and after every visit to the toilet. You can also buy a powder containing piperazine from the chemist which you take as a one off dose and repeat 14 days later.