Feel constipated, and only able to pass soft thin stools. Could this be some sort of interstinal infection? I eat high fiber and use Metamucil daily.

Colonoscopy. Any changes in bowel habits calls for seeing your doctor. I would recommend seeing a gastroenterologist for a colonoscopy irrespective of your age. Of note everyone at age 50 should have their 1st colonoscopy for colon cancer screening.
Maybe, or not. Thin caliber stools can be seen in stress (irritable bowel syndrome), constipation (inadequate fiber and/or fluid), diverticular disease, gyn diseases, as well as more sinister problems, like cancer. Don't know you, age, risk factors, bowel habits, etc. Call your doc.