Possiable to have a neg blood test?

Dr
Has anyone else had a similar experience?
So I thought I was preggo after 5 faint positives and several days late for my period. At first I thought I was having a miscarriage but I had no cramps. Not one. So I called an advice nurse and they told me about break through bleeding, I felt better for awhile but the next morning I woke up feeling very doubtful, I ran to the store to go buy a pregnancy test thinking if it came back bfn then It must be a Chem preg.
  But a small voice inside my head kept saying, "don't test it WILL come back negative" 
Generally I listen to that voice, it's saved me from many dangerous situations. But I had to test. Five stores later I finally found a first response brand and I tested negative.  
I called the advice nurse again later because of (what I'm guessing now to be) an anxiety attack. In fear of ectopic pregnancy they sent me to the ER where they did a blood & urine test and a vaginal ultrasound. They never used the fancy ultrasound the gives the better images just the traveling one. Everything came back negative and they sent me home. 
But I've heard that break through bleeding can cause you to have a bfn because of the hormoans for the period is stronger. And I was only three weeks. Way too early to see anything on a weak ultrasound machine. I think there's a good chance I'm not pregnant so I'm going to keep trying, but I am I'm only three weeks, so even with a blood test, could that be too early? 
I don't want to refuse to acknowledge the truth, but I'm still experiencing symptoms and that little voice that told me not to test is bugging me.
Has anyone else experienced this? Has a neg blood test and still been pregnant? 
I apologize for the length I just felt that the whole story needed to be shared.