What Causes Difficulty Urinating After Removal Of Prostate?

Hi I had a surgery on 01/20/15 (removal of prostate) after surgery I was urination fine and I didn t have any problem until few days ago I started having problem again when I urinate. I m back again to the beginning before the surgery and again I barely can urinate (is just dripping) and I would like to know what could be decreasing drastically again the flow of urinating. Thank you! Moe