What Causes Lower Limb Pain And Frequent Nose Bleeding?

I m 15, and in the last 6 months, Iv e been bruising very easily, a bump that causes no pain, or even my friends poking me, leaves a big bruise, I ve also lost a lot of weight 23lbs (was 141lbs, 5 8) and my appetite. I am extremely fatigued, staying awake for periods longer than 4-5 hours exhausts me, I get strange, sharp, exruciating pain in my lower limbs, and I often notice my nose bleeding. My periods have stopped, which I think was because of the weight loss. I know this sounds odd, but my intuition is telling me I have cancer, which would not shock, nor scare me, as there is a long family history of a variety of cancers. I look like a skeleton, I sleep like a new-born, I find at least a dozen new bruises every day, I cant eat, and my nose bleeds 2-3 times a day, and my parents dont care. Theyve put it down to, me being obsessed with my figure, being a lazy teenager, being clumsy, picky, and picking my nose. Apart from the fact I am a teenager, none of that is true, they wont take me seriously - or too the doctor - and I think I may actually be, literally, dying, and if I m not, its sure looking like that may be true by the end of the year if I keep fading like this. I m 14, I have no money or credit cards and it has taken all of my energy to write this, please give me some advice.