What Causes An Altered Sense Of Smell?

i had radiation therapy around 15 yrs ago and take thyroid medication,my last check up showed a very low level of thyroxine so the Dr increased my dose as i was very tiered,losing my hair and my stomach has been enlarged that was in june i have not improved.but have noticed that i have a rubbery type smell to my hands i have had this before when i have felt run down what causes this