i feel im pregnant but tests say negative

I had my last period March 16, 2013 and it was rather heavy. The heaviest one yet. My husband and I have been trying to concieve for a while now, I'm a mother of 10 month old twins, but my last pregnancy was similar. Like, i didnt know i was pregnant until i went to the doctors, they told me i was already 8 weeks and it's weird because all the home tests I've taken were negative. I didn't have the gut feeling either. But now I'm having a gut feeling that im pregnant and all 6 of the home tests I've taken came out negative. My periods are irregular so it's hard knowing. I've only had a few symptoms like wanting to eat eat eat, very very mild abdominal pain, sometimes a sharp sudden pain through my stomach, frequent headaches, frequent stomach aches followed my nausea. I just don't know, somebody help?! :)