What Causes Crawling Feeling In And Out Of The Rectum?

Over 4 years ago I had what I think was a parasite - I had all the classic symptoms of pinworms, however could never see anything. I could feel something crawling in and out of my rectum ad eve into the base of by vaginal area. I tried the reese s pinworm medicine and within 48 hours felt significant relief. Then a few weeks later all the symptoms came back. I eventually saw a doctor and he gave me what they give horses for parasites. He said he found no evidence of worms but if I had a parasite the horse pill undoubtedly would work. I took one pill, then 2 weeks another. However the symptoms still seemed to be coming back or to over. Within a week after that 2nd dose I had a major surgery and never had the symptoms again. Between this past Thanksgiving and Christmas I started having similar symptoms and I am terrified because the previous episode lasted 9 months. Someone suggested I rather have internal hemorrhoid however I don t have any pain or bleeding. I have had 2 hemorrhoids in the past outside the rectum but no itching or burning. This time I read a doctor s forum and it was mentioned by one physician to effectively get rid of worms you need to take Rees es twice a week for 2 weeks, which I did. But the symptoms keep coming back. At this point I feel desperate. I cannot see anything.