My 3 year old son complains about having an itch inside his bum, i though it was worms so i gave him worm medicine but nothing has changed. he cries all night pls help?

Threadworm/pinworm: These threadlike human only parasites live in your colon. The pregnant worm exits the anus & lays eggs there in a glue like substance that causes a rash/itching. You can help the itching with a cold water wash & hydrocortizone cream. Any worm treatment can kill the worms but the itch remains until the skin rash is gone. It can also be from yeast, group A strep or other causes. Doc may need to see.