hello leah, as i perceive you were treated for breast cancer at age of 18 . Sometime has passed since then and now recently you got breast reconstruction done. and Now you are observing hair fall. If my analysis of case is correct you have not received any chemotherapy recently. Hence your hair fall is not related to chemo. Now such patchy hair loss could be because of multiple of things out of which following few are more common.1. as response to some recent stress in last three month including the surgery. 2. New onset alopecia areata which could be autoimmune based and unrelated to your previous disease. 3. Nutritional deficiency like anaemia or worm infestation. 4. Endocrine disorder like hyperthyroidism Based on pattern of hair loss differetial can be narrowed down. However another point from my side is, If you had breast cancer at that young age than you should undergo genetic workup to cancer predisposition However as that is not the present point of discussion, so i will leave that point for further discussion at some other time in future hope it answers your querry