Missed period after thyroid meds

So, I had a c- section 8 months ago and got my tubes tied at the same time. It took 4 months for my cycle to resume as normal. I've also got a slow thyroid and began taking those thyroid activators from the health food store. My next period after starting the pills was two weeks long and heavier than usual (this was June). Then my period stopped altogether until the other day when it finally came. OB dismisses the whole thing but I cant help getting the feeling like something's wrong. Anyone else had this issue or similar?