I'm 31 and getting periods since age 13.they were always regular except from Sept 2011. I was 12 days late.anyhow.April 2012 got diagonsed with Hypothyroidism.Being put on generic Levothyroxin 75mcg periods became regular exact 30 days.My GP changed medication from generic to brand Synthroid 75mcg from last 3 weeks.Peroids were due on 18th but today is 24 still no sign.started spotting on 23rd but it's so scanty and mostly old blood that too on cleaning internally only.Took 3 pregnancy tests all negative.. been trying to conceive for 4 months... I'm so frustrated.. don't know what to expect... please anyone sailing/sailed in same boat...