after gaining back 3 pounds after reaching my goal

I had went on a vacation and gained 3 of the 56 I lost back. I was very upset and kept trying to get it back off with a no luck. Then I went exercise crazy for a week and they all came off. But as soon as I went back to the maintenance calories each day they came right back on! I don't understand why and I'm feeling so lost. When I eat what I am supposed to its like it's too much calories and then when I eat to lose a pound a week I stay the same.... I need help.