I had a clear light yellow ribbon-like flat string pass in my stool, it wasn't long, and didn't look segmented but i'm worried. i've recently been having multivitamins and that also made my urine come off as bright yellow, similar to the flat string?

If you live in the US and have not travelled to a poor country, you are vey unlikely to have an intestinal worm. Yellow colored urine when taking vitamins, including Riboflavin, is normal. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV, vaccine.