How can I stop overeating?

I have been overeating so much lately! I feel like I'm gaining weight, although I haven't weighed myself in a long time. Last time I checked I weighed 135 at 5'9". Anyways, I think I'm much more than that now. The cold weather makes me not want to exercise as much. I usually eat a healthy breakfast (cereal, milk and a piece of fruit) and an okay lunch (peanut er sandwich and carrots with hummus). Then it gets out of hand! I sometimes have a healthy snack like an apple but I usually find myself eating mindlessly, like cookies or something! What should I do?