I went to the ER the other night with severe back pain. I thought I had a kidney stone again. Well after CT scans and X-rays, I had no stone but my colon was very "full." They gave me Mag. Citrate to drink. I drank the full bottle 2 days ago. Nothing. So I took some Dulcolax. Still nothing. This morning I drank another full bottle of Mag. Citrate. Nothing yet. Does anyone know how long the Mag. Citrate takes to work? Any advice?