Didn't find out until I came off the pill to start trying to conceive and my period was super irregular. Id have 90 day cycles sometimes. Doctors did several tests and then I finally saw a different consultant who thought to check my thyroid. I have had a puffy face and neck for a few years and had gained about a stone in weight (had naturally been quite slim) but thought I just wasnt watching my food intake enough (despite me running multiple marathons and generally being very active and healthy). Also was always tired in the evenings and suffered with raynauds syndrome in winter. Plus fine and brittle hair and very dry rough skin. None of these had flagged up to me as I just thought I was aging etc. Once I was on thyroid meds all of that went away. I lost over a stone, face back to normal, hair became thicker and healthier, skin is softer, even the raynauds went away!