Am I Losing Too Fast

I am Pre-Op And I Had My Consultation last Wednesday 3/15/17 With My Surgeon And He Asked Me To Lose 50Lbs Before He Do My Surgery or Give Me A Date(Not Insurance Required) He Also Told Me It Would Probably Take Me 6Months But I Told Myself I Can't Wait That Much Longer I'm Ready Now So When I Left I Started My Diet And Exercise And So Far I Have Lost 19.7Lbs In 6Days Am I Losing Weight To Fast I Feel Fine And I Think I'm Getting All My Nutrition I Eat Anywhere Between 600-1200 Calories A Day(Lettuce, Tomatoes, Tuna, And Fruit) I Drink 2 Protein Shakes A Day(Included In The 600-1200 Cal. intake) I Drink About 3 Liters Of Water A Day And I Workout For 1-2 Hours At The Gym. Am I Moving To Fast And Losing Weight To Fast Or Is This Normal And Ok I Actually Have A lot More Energy Than I Did 2Weeks Ago I Feel Really Good And I'm Loving This Lifestyle I'm Adapting Too.