Bouncing Between Weights?

I normally weigh myself once a day, normally in the morning after breakfast, but I've been bouncing between 215 and 213 for the past week and I have no idea what I'm doing. I normally stay below my calorie intake and try my hardest not to eat such fattening foods but I keep gaining 2 pounds and then losing it all the next day. I was just wondering what I could do to lose more weight. I've lost 17 pounds so far and I want to keep losing more but it's getting weird...