I hear you! For my first marathon I PUT ON 4 POUNDS! I was mad! My husband had lost weight but noooooo, not me. What I can say is that you cannot just rely on the scale. You must also take into account body composition, (body fat%) and your BMI and things like your actual measurements. All those combined give you a clearer picture of fitness. I gained 4 pounds but dropped several % points of body fat. So even though I weighed more, I'd loss fat and gained muscle. There are some tiny women out there that weigh much more than they appear because they are solid! Go by how your clothes fit and how you feel, that what matters most! Good luck to you on your first marathon!