I would feel funny discussing these things with my MIL as well, but for me it's because she is very critical of me behind my back. She's the smile to your face and cut you to the ground when you walk away type, and her daughter is the same so anything I do is just something for them yack to each other about. SIL lost over 100 lb. and has put it all back on...and now that my loss is noticeable they don't say anything, they just stare at me up and down like I'm grotesque or something. It makes me extremely self-conscious and uncomfortable, but soon as I make eye contact they smile and chit chat, then back to staring me up and down and whispering as I leave the room.
Oh, and hubby told MIL the other day I was going to buy new pants this weekend because mine were too big and she said "oh, I have some 20s that are too small for me now, she can just have them." He said this to me and I said no, 20s are what I was falling out of, so she offered she has some 18s that don't fit her anymore...I went to the store today and I am in a 16 now, so he told her this on the phone today that I wn't need her 18s and he said she got real quiet then said "I doubt she's in a 16, but don't tell her that."

I have 2 brand new pair hanging in the closet to prove it, and they fit me perfect. This is just to say that you should count your lucky stars...they are going to talk no matter what, better it be to your face than behind it.
Honestly, it's worse to be gawked at while they refuse to acknowledge my weight loss, than it would be for them to say something! I am uncomfortable either way, but being stared at like that is really awkward for me.