What Causes The Fall Of Eyelashes?

im 23 years old i have hypothyroidism ( underactive thyroid) however ive been taking tablets for it for over a year, I have low iron ive been taking tablets for 3 weeks now, my eyelashes have been falling out around 8 today and a few yesturday. im frightened they all will fall out. please help im scared ill be bald eyes by tommorrow. how long do eyelashes take to grow back. please reply.