My eyebrows don't grow back like they used to what can I do to make them grow back? I'm only 18 I don't pluck or wax they just fall out on their own

Get checked. There are some health issues and nutritional deficiencies that can lead to losing hair. Underactive thyroid can cause loss of the outer eyebrows. Low iron stores and low vitamin d can lead to hair loss. I recommend seeing your doctor and getting checked.