After pondering your dilemna - I think you should go about this scientifically and
try it two nights in a row and see if your weight increases accordingly - if so try it again on the third night - keep on till you quit gaining - your husband will probably be very happy and will chase you around the house (so you will lose those pounds and go about the process all over again)

Seriously though - I doubt sex makes you gain weight and definitely not 2 or 3 pounds every time. It must be some weird co-incidence - again what are these pre-occasion dinners - something salty?? or are they not LC meals?