Just my 2 cents, but if I weigh myself after eating a full meal, I'll easily weigh an additional 1.5 pounds...
You probably didn't gain weight, I recommend weighing yourself at the same time every day to ensure a similar amount of food is in your body. 1.5 pounds is nothing. Eat a steak, brocolli, sweet potatoes, and a couple glasses of wine, that's easily 1.5 pounds, if not more.
Not sure when you started this routine, but I also recommend weighing yourself weekly. It's nearly impossible to notice improvements day to day.
Eating dinner at 6pm, skipping breakfast, and eating lunch at 12pm will give you 18 hours of fasting. That is often my routine on IF fasting. I never feel famished, I'm guessing because I sleep through half my fasting and regain energy that way.
Stumbled into Primal due to food allergies, and subsequent elimination of non-primal foods.
Start Gluten-Free/Soy-Free: December 2012; start weight 158lbs, Ladies size 6
Start Primal: March 2013, start weight 150lbs, Ladies size 6
Current: 132lbs, Ladies size 2
26lbs lost since cutting the crap.