I have had that same feeling too. I felt like my left pelvic bone was cramping and it felt very stitch-like. I got scared that it could be something sinister so I went to my doctor. He said that at my age (21) I shouldn't worry about anything bad. He also said that I felt a little constipated and that I should change my diet; veggies, lots of fibre and LOTS of water. I've been doing that and ever since he eased my mind my symptoms had vanished! I haven't thought about them since!
At your age, I would not worry about anything bad. :) If anything, it may be an ovarian cyst which are relatively common and the vast majority of them are fine! Don't fret, pet. <3
Also, is it a feeling that comes and goes or is it constant? It may just be you ovulating.