First of all.stop comparing your loss to that of your sister. Everyone has a different metabolism.
Next, please post a detailed menu (with quantities) on this thread so we can all take a look at it. Perhaps we can spot something amiss.
Pat yourself on the back! A 17 pound loss in two months is not at all shabby! An average of two pounds per week is a good safe rate of loss. Right now your body may be doing a bit of a re-org before you drop more.
Hang in there and come here to get and give support. We're all in this together.