My period was supposed to come two weeks ago!

Hi everyone, 
So my period was supposed to come two weeks ago... 
I can't exactly remember when my boyfriend and I have had sex but it has definitely been about 4 times in between the time I last got my period and when it was supposed to come. 
I have taken two at-home pregnancy tests and they have both been 'negative', however I'm still so worried!
I went to the doctors yesterday to see if I could get the pill but they said I may have PCOS (polycystic ovarian syndrome) or a thyroid dysfunction, and therefore I have to have a blood test. My doctor doesn't know that I'm sexually active. 
What do I do? 
Please help! Does anyone have/know of someone who has had an absence of a period this long? 
Side note: I haven't been very stressed lately, and my weight, exercise etc has not changed. 
Thank you so much, any replies at all would be greatly appreciated