Mental Issue?

Ok, so my problem isn't as bad as so many of yours here on this website. I feel kinda selfish for posting this when most of you are going through tougher and harder times than me of having worse problems but I want to hear input on this. Ok well this problem of mine has happened to me for a while. It mostly started in 7th grade but it wasn't a huge deal. I just shrugged it off. Now, when my first ever boyfriend asked me out in September 2012 I never even dwelled on it since I was so happy. Then he dumped me in October. It was four days before our one month anniversary and he had ignored me for three days. This boy had said he loved me and all that stuff then just broke my heart. Did I mention it as the same day I left for the one field trip I was looking forward to for the whole year? Well, I fell into a depression. I was sad all the time and I couldn't stop thinking about him. I would cry almost every night and think there was something wrong with me. It was then that my problem became maybe a mental problem. It was about body figure. Fat or not. I'm a runner and...well...very self-conscious. As a runner, I'm underweight like most runners are and everyone says I'm skinny. But there are times that I look in the mirror and become absolutely horrified, thinking I am fat. I have these mini depressions that will usually go away. I have told myself that I was going to become anarexic then the next few minutes I would look back at myself and think I'm skinny and there is nothing to worry about. Note that I'm totally over my ex. But I keep thinking I am fat then the next few hours, minutes or maybe even day(s) I am skinny. I have told myself before that I would lower the amount of food I ate and exercise more to get a better figure and then tell myself I don't need it. Am I in danger of getting an eating disorder? It is kind of scaring me and I am very aware of these weird mood and mental swings. Any thoughts?