No period for seven months and not ually active?

I'm fourtteen, and I know it's normal to have irregular cycles at this age, but seven months?! Every once in a while I get period symptoms (cramps, moodiness, headaches etc) at the most unpredictable times, but with no period. I am NOT ually active, at all!! I know my mom had something wrong with that, and had to get operations, but I'm not sure if it's hereditary or what. Yesterday I got a tiny bit of blood, but nothing else, and that's happened before. I've had my period since I was 12, and I didn't have it regular but it was more normal than THIS! What's wrong with me?!