I pulled what I thought was about a 10 ft. Tapeworm out of my anus. The lab ran tests and said that I didn't have parasites. What could it be?

Repeat the studies. Did you give the lab the 'worm', or did you just do stool studies for eggs? The latter can be negative and should be done on earolyn am sample on rising. You might also apply scotch tape to your anus before getting up as well as supplying an early am stool specimen. Check with your pcp regarding other symptoms of parasites and a CBC looking for eosinophilia.