17 days late...

Kinda confused as to what is what....

I am 41 with an eleven year old child. I have adenomyosis, which results in extremely heavy flow, and slightly longer periods. My cycle is very regular though, coming every 29 days like clockwork. (been that way since a teen, even so much as to have a period exactly 29 days after my child was born). Other than a twinge here and there during my period, I have never had any of the "normal" symptoms, pre-menstrual or otherwise.

My last period was 06-26-2011. I am currently 18 days late. Took pregnancy test on third missed day, then again 4 days ago, both negative. Have been feeling nauseous ALOT, fatigued, my nipples are constantly sore, a few days had achey lower back, and my bladder appears to have shrunk as I seem to be peeing constantly lol During my pregnancy with my daughter I was nauseous the first 4 months non stop, and it feels alot like that. When pregnant with her, I found out two weeks after conception due to a pre-surgery blood test (Obviously no surgery for me!). I never took a HPT, so not sure how pregnant I Would have been before it showed positive on one.

Was wondering if I could still be pregnant even though the HPTs are coming up negative. Just weird to me how i go from an every 29 day heavy flow, to 47 days and no flow. I have no signs of anything else wrong. At my OB checkup a few months ago, doctor said menopause is a good 15 years away, so not worried about that. (My mother didn't hit menopause til almost 60, and my okdest sister still hasn't hit it at 52.) Any thoughts?