Too few calories?

I've been lifting heavy weights for six weeks now. I've heard you need to eat more to continue losing weight while lifting heavy. Muscle burns more calories than fat and you need to feed the muscle adequately. Otherwise you don't build muscle and you stop losing weight. So every so often I eat more and then I lose more weight. It's been nice. But it's hard to retrain my brain that it's okay to eat more. Usually the times I eat more and lose, it wasn't planned and I think I overate. Then the scale moves down. It appears I need to eat more.
For example, Saturday was a rest day because it was too busy to work out. I rearranged things and it was a scheduled rest. I had a bridal shower and then a coffee date. I ate WAY too much. Not healthy foods either. I had a croissant with pulled pork, potato chips, punch, and TWO pieces of cake at the shower. I kept eating candy at my parents' house. Dinner was cheesy broccoli soup and a small bowl of ice cream for dessert. And then I snacked more on the drive home. Needless to say, I was scared to see the number on the scale the next morning. The crazy thing? It was 143.0. The lowest number since Nora. Other than when I had the flu, it's the lowest I've seen since Ella was born, possibly the lightest I've been since Steve and I got married. In other words, I ate a ton of sweets and crap and the result was I was the lightest I've been in probably 6 years. Confusing, no? Guess my calories were a bit too low. I'll increase them but try to eat healthier than on Saturday. Some parts of weight loss really are counter-intuitive. I'm definitely not complaining though. :) Bring on the food!