Been taking 2mg flm a day for about three months..how long will take to leave blood..my doctor ordered blood work from lab for drug screen?

What medication??: assuming that "flm" means film, I will further assume you are talking about buprenorphine (suboxone/subutex) 2 mg per day. This is a very long-acting drug, albeit in a low dose, but it could be present for significant amount of time. Blood is actually not the appropriate place to look for most drugs, with a few exceptions - Suboxone is not one of them. May be present for several weeks.