I Am A 55 Year Old Woman And Losing My

I am a 55 year old woman and losing my hair. It is blond, used to be very fine, but thick. I started to notice it thinning and large amounts in the shower drain about e years ago. It was waist length, so I cut it to shoulder liength. It became much healthier, but was still falling out. I didn'the feel well for many months and was finally diagnosed with anal cancer in July of 2015. I had chemo and radiation, which ended until December of 2015. I am cancer free, but the hair loss is now extreme! It is shorter and shorter and so thin I can barely make a pony tail as y hick as a child's finger. What dr. or where do I start tI find out what to do or if I just need to buy a lot of hats? Btw..I did not loose hair during chemo.