...they are falling off me!? I bought 36 inch jeans for my 39 inch waist and in a hour after washing they are falling off me.

Good ol' LEVIS 501's or 550's have zero stretch factor. And they haven't gone out of style for over 100 years.Just take into consideration the shrink factor. I've forgotten what it is. I think 1" in the waist and 2" in the length. But ask the sales person to be sure.Good Luck baggy pants!