Recently have had tiny black specks in stool now have tiny black strings in stool. have been drinking warm lemon water and eating yoghurt?

See a GI specialist: What you could be seeing is blood in your stools. I would see a gastrointestinal specialist asap, to make sure there is no bleeding ulcers in your stomach. In the meantime, i suggest stopping the lemon water and any non-steroidal anti-inflammatory medications, such as advil, aleve, (naproxen) motrin, ibruprofen, goody, or bc powder which can worsen bleeding.