Don't feel discouraged... it was only one day. I just went on a 3 day binge of junk food but I'm excited for tomorrow so I can set some new goals for myself. Seriously log your food and look at what works for you! If you are eating healthy foods you get to eat way more! You've already lost 3lbs so your well on your way - its a work in progress!
And come here often for support and motivation - AND to keep you on track!