How do I go from snacking several times throughout the day to having three main meals?

I think you have to start thinking of meals as a treat to yourself. First just try eating one filling meal each day (slowly absorbed carbs really help with this). You will notice that you will crave food less, because you actually fulfilled your body's need. We all know what is healthy, but I just think if instead of "I didn't do it again, I suck", you think: "Even if it's one meal today, I will treat myself, because my body deserves good treatment", it will tie positive feelings. Instead of "just one" you'll see "plus one" thing you do for you. It worked for me.

Whenever you have cravings to snack, tell yourself you can snack but you must wait at least 30 min. You’ll find that your craving have disappeared in that amount of time. Also make sure your eating a enough calories during those 3 main meals or your risking a binge.