Why am I so dang hungry all the time?

I had an 2 egg sandwich with cheese and veggies for breakfast. It didn't quite hold me over (!?) so I had a handful of sunchips before lunch. Lunch: salad with veggies, bread and cheese in it, should've been filling but I was still hungry after. Have been talking myself out of a snack before dinner. Dinner will probably be cereal with fruit and milk. I'm an overweight woman.