What Causes Delay In Periods,nausea,headache And Bloating Of Stomach?

I recently got married in June of this year. I have never been on any form of birth control. The 14th of August was my last normal period. My next period should have been on the 11th of Sept. and then again on the 9th of this month (Oct). I have ALWAYS kept track and been 29 days on the dot.. Even under large amounts of stress and life changing ordeals. I have taken 3 home pregnancy test, and went into the doctors 2 days ago for a urine test as well. (No Blood Testing)I have recently been experiencing Nausea out of not where, more sleepness than normal then when I do sleep I find myself waking up 3-4 times during the night, slight cramping like I'm going to start my period, slight dizziness even when I'm just sitting, nipples are tender to the touch, Headaches almost every day (Which is NOT normal for me) Gas and Bloating, and a small amount of weight gain. Even though I have taken a Urine Test with a Doctors office is there still a possibilty I could be pregnant? Or should I be thinking is something else at this point? And I do have a full check up on Monday but I was wondering if I could get some better answers because no one has really been able to tell me much of anything.