Trying to Counter-Act Frustration with Positive Thoughts

It's getting harder and harder to lose weight for me. x_x
When I first started working out in July I was only going to school for a light 2 days a week and I'd spend hours at the gym. I lost a steady 1 to 2 pounds a week for almost 3 months when I started at 158. Then I went on a vacation and came back to a heavy school load 3 days a week and it's much more difficult to find time. Now I stay the same weight for weeks and weeks. I'm at 141 now with a goal of somewhere around 128. So it is kind of frustrating.
But I keep reminding myself that "I've lost 16 pounds over all. That's SO much more than I've ever lost before from dieting/working out or anything. I'm sticking with it and making it a lifestyle instead of giving up after a couple months like I have before. Everything I'm doing is more than I've ever done." So that helps.
But it is still kind of hard. I'm not always great with my diet, and I know that the smaller you get the harder it is to lose weight. I'm only about 3 pounds away from the "healthy" margin of BMI, but I still don't feel that small! I wonder if I'll ever get to my goal weight. :/