Drs Appointment

So I went to the Drs office today to talk to her about why I've been having VERY VERY irregular menstrual cycles & VERY VERY long ones when I did get it. Long story short she's making me have a bunch of labs done. Thyroid is one of them. I don't know what exactly that is. I feel stupid asking, but could someone please enlighten me. I didn't ask her because she already looked annoyed. She also said if I'm TTC to start taking these vitamins. Anybody else take them.? (This is a follow up post to another I made about a month back about having been on my period for a month)