I have had an underactive thyroid now for approx 6 years and have gradually increase my medication to 150mcg Lethothyroxine. Recently I have been experiencing mood swings and feeling down quite a lot with no real reason for it (I have a nice life!!). Also, my period has become irregular which has never been the case for me. This month my period came only for 1 day which was really slight and then disappeared. Thanks