What does it mean when colon polyps are continuously produced with dysplasia

I have done three colonoscopy in last three years. Five polyps were found/removed in April, 2007, in which one polyp (0.4cm) in rectum was found to have high grade dysplasia. Next year, there were seven polyps (from 0.2-0.3cm) found, all had moderate dysplasia. on June 11 of 2009, three polyps were again found in my sigmoid colon, and all had moderate dysplasia.
My questions are:
1. Why polyps have been grown so fast in my colon, particularly why the polyps found in the last two years all had moderate dysplasia? Does it mean that there are some demons in my digest system or in my body that have been making these pre-cancerous conditions in  my colon?
2. Do I need do some further exam, such as CT, ultrasound scans or CA19-9, CEA blood tests to exlude some potential bad causes in my digest sysytem or other related part of my body?
I am looking forward to having your professional opinion and advise because I am really worry about the pre-cancerous conditions in my colon. Thank you. Victor