I had a sigmoidoscopy 3 days ago & haven't had a bowel movement since 4 days ago. Is this normal? I started back on lactulose & fybogel.

Chronic constipation. Sounds like you are chronically constipated, given the meds you are on. Constipation can be from diet, meds, anatomical, neurological causes. Left colon gets cleaned out with enemas for a sigmoidoscopy. This may all be normal for you, but don't have any details. Call md who did procedure, report in.