As it turned out, there were indeed coupons for Sunday, and every subsequent day for that matter.
Every day of the month had their own specials going on, with particularly large ones for the 31st, which made sense given that would only occur seven times a year.
And the deals were simply extravagant. Restaurant meals, delivery places, grocery store treats, and all at such a discount that your food bills had shrunk to nearly nothing. The portions were nothing to scoff at, either, generally starting at large and approaching the level of absolutely ridiculous. Even with your herculean ability to eat, there were times you couldn't finish your meal, and had to save it for leftovers.
You'd made a habit of bringing many of your discount goodies to work with you. Your job in data entry was anything but exciting, but made for a good place to snack on your many treats. The boxes of snack cakes were easily your favourite, and it was rare that you didn't bring a case and finish it over the course of the work day.
As you predicted, you never needed to pack a lunch, simply eating at whatever restaurant the coupon book had for each day. You only had one problem with that, and that was the need to finish off everything you ordered, which was often quite considerable. You had gotten leftovers from lunch the one time, and left them in the breakroom fridge. By the time you'd gotten off work, though, your doggie bag had disappeared from the ice box, and of course no one knew what had happened to it. After that, you always made sure to fit it all in your cavernous belly, even if it left you sore afterwards.
The weekends, though, were by far the worst of your days of gluttony. Between several restaurant and take-out sales, and the need to finish your leftovers before they spoiled, you basically spent the day eating full pelt, minus your naps.
All this over the course of the last month had a few obvious results. One, your stomach was forced to stretch out, allowing you to eat more. Two, as your stomach's capacity increased, your appetite was following suit, meaning you had to eat larger portions more frequently in order to feel full. Three, and perhaps most obvious, was that you were starting to gain weight. What first alerted you to this fact?