The only thing odd to me is that being overweight as much as you are (don't take that the wrong way) it is much easier to lose weight in "chunks" so to speak so it does seem strange that you haven't lost weight in that timespan, yet you lost 2.5 inches off your waist. Just odd numbers overall to have that happen in relation to your body composition.
However, if that is the case and you have lost that amount off your waist then there is really nothing else to worry about.