Is it normal to keep fluctuating from weight to weight?

I diet a lot and run a lot until about two weeks ago I go an injury and had to stop exercising. I carried on eating a pretty healthy diet but i find it hard to maintain and so i crave food. For two days, I have eaten crap and so I am trying to get back on track. Within the two to three days though, i have gained 3 kg but whenever i start dieting again (and recently exercise again that my knee is recovering) i can lose it in 2-3 days too? Is this normal?
I would just like to lose weight and maintain it, but it just keeps going everywhere!