It is perfectly normal and you shouldn't worry about it unless it is a big cramp or very painful. It is because when the egg comes out, sometimes some people can feel it. Sometimes it can be at the right hand side and sometimes can be at the left.
Some people have signs to know they are ovulating such as slight pain, tender breasts, increase of sexual drive, and etc. The best way to find out when you are ovulating is by taking your basal body temperature and observe your cervical fluid everyday. If you are interested to find out more, I strongly recommend all girls to read the book called "Take Charge of Your Fertility". It is a very good book for you to understand your cycle and your body reacts differently during your cycle.