What Causes Stoppage In Menstruation?

Hi please could i ask a question. I am 26 years and have been on and off the pill from the age of 15. I decided to stop taking the pill via the injection back in early december 2010, its now nearly april and still no period? My hair over the last few months has started to thin and my skin is either full of spots or under the surface little pimples. My cheeks also look lined when i smile like they have lost there elasticity, i am beginning to become concerned