Missed period? Virgin?

Okay, so I'm 17, and never had sex. My period is usually irregular I've missed it by a few weeks and a few days. I had my period in September towards the end of the month it was very light, and had clots. It kind of worried me, but usually my periods aren't that bad, minimal cramping and usually light. So I thought nothing of it and didn't try to stress over it. So October goes by and I didn't have my period which is kinda of odd. It's November now, and I still haven't had my period. I've never had sex before so being pregnant is kind of out of the question, but it still worries me a lot that I could be for some reason. I've been kind of constipated/gassy for the last few weeks, but I think that's due to me being slightly lactose intolerant. I will admit that I am overweight, and don't exercise much. And I was suppose to get my blood tested for thyroid issues awhile ago, but I still haven't gone because I'm scared of the results and I'm scared that I could some how be pregnant. I usually have my periods at the end of the month, so I'm going to wait it out a little longer till I go to the doctor. I've had some symptoms of getting ready to start my period this week so I think it might come soon. But I just want to know what could be wrong? Sorry I rambled on for so long, this is just really stressing me out.