Super Late Period!!!!😒😔😞

So I've been late in my period and I don't know what's the cause. I know I'm NOT pregnant but I've been getting worried lately. The last time I had a period was in September 2015 and still haven't came in yet. I've went to the doctor and asked questions; they say that everything is okay and that its normal.... I REALLY don't believe that. Can someone please help me. I really need a answer. I'm about to lose it.😔😖😔😖😞😖