What Causes Dry And Brittle Hair And Nails?

I have not felt like myself for at least 6 months and every day it seems worse. I am ALWAYS tired. To the point it's hard to stay awake even at work. My legs swell easily. My hair and nails are very dry and brittle and my hair is thinning. My memory is terrible now.... Not sure if it's because I'm so tired or if it's my actually memory. Not to mention weight gain. Could be that I am not as active as I was. before I was tired all the time