cadz

Hey my name is Cadyn and I turned 18 july this year, for the last 8-9 months I have experienced a slow thinning of hair all over. At the start of the year I had a full head of bright brown hair which was long ( thin ) but a lot of it. I started using WAY to much product through the course of a few months and suffered from a pretty hard case of seborrheoic dermatits. I eventually after 2-3 months fixed my dermatitis and now it is still under control apart from a very mild break out every so often. The entire year i stressed every day, and eventually became mildly depressed because it affected my self-esteem. anyhow after fixing my dermatitis I thought my hair would start coming back thicker, but it didnt. ( also I receeded very slightly through out the year ) .. it is quite strange because I receeded about 2cm but them almost 1cm grew back radnomly. I want to know what it could be, I went to dermatologist and she told me .. nothing .. then I saw a doctor and he said it could be the dermatitis or something but I don't know. Yesterday I shaved off to a buzz cut because my hair was so uncontrollable it would make me very sad easily I want to know why my hair is thinning all over, its not in the family history either.. someone help me please?