Irregular period and contraception

If the menstrual cycles last longer than 35 days (in other words, if your period occur once every 35 days or more), the condition is called "oligomenorrhea", or rare periods. Oligomenorrhea is a sign of hypogonadism. In more extreme cases, lack of a period for more than 3 months is called "amenorrhea". Amenorrhea is one of the signs of anorexia nervosa. Anorexia nervosa is considered a psychosomatic disorder.
You may consult a gynecologist inquire about best solutions for birth control. In cases like yours, contraceptive pills are usually given to normalize the menstrual cycle rather than to be used strictly for contraception.