I Am Infected With Giardia. I Have Read Several Articles

I am infected with Giardia. I have read several articles and found that Giardia causes diarrhea, but my problem is something different. After first bowel movement, it stops moving and stool remain in my colon. It is very hard to expel even after a lot of efforts. My stool is not hard. It is soft then why does my bowel movement obstruct? Can Giardia obstruct bowel movement?