What are these white things worms in my stool? What are tests for pinworms?

Your doctor can . A scotch tape test can be done for you. You set your alarm to wake up in the middle of the night (when the pinworms are usually active) and press a piece of scotch tape to your anus. The tape is then stuck to a microscope slide and the laboratory can look for pinworm eggs. A stool sample for ova and parasites is not as good a way to diagnose. Some just do presumptive tx if exposed.
Need exam of stool. Pinworms usually produce severe itching, particularly at night, around the anus. A scotch tape test looking for the worms is the best way to diagnose this and is fairly simple. No way to know what the "string looking things" are without some tests.