I Take Lorazepam 1mg Tablets 4x's A Day I Got

I Take Lorazepam 1mg tablets 4x's a day I got a Urine Test for the last three times and they come out negative that I didn't have it in my system, how can that be I take them every day Faithfully? Now they are taking them away from me and giving me something else because they don't believe that I am taking them! Can you think of something that I haven't, Please Help!!