hi, well first of all if your butt is flat,you can't really make it poochy(just the way you're made), but you can make it look better and not droopy. i don't know how you're built or if you have a workout routine but from experience i can tell you do some cardio(if you lose weight quickly or slow it varies on how much or long to do it). so i'm gonna say to do at least 15 to 20 min. 3 to 5 times a week to start, then go to 30 to 45. switch up. like a couple of times a week do 20 to 30 min. of walking or some kind of cardio and the other day or so try to do 30 to 45 min.also do squats(really good for the butt)when you walk try to squeeze your butt cheeks. you can do lundges and i like to stand(or lay down ) up put my hand on something like a chair for balance and swing my leg forward and backwards and forward and kind of to the back and side. do this at least 20 times each. if you can to start. or 10 if that's too much. well good luck.