I Am On Drug Court And Get Regular Drug Screening,

i am on drug court and get regular drug screening, for the past 2 months i've been getting diluted urines and i onlyndrink about 40 ounces of water a day and never before my test. i am also diabetic on insulin, brittle dibetic. i also have rheumatoid arthritis, and was recently put on arava, why does this keep happening/