10 weeks 2 days pregnant and heavy bleeding?

Yesterday i went into the shower it was warm like usual and i started to feel extremely dizzy. I had to lay down 30 mins Then i sneezed and it felt like a huge rush of water came out. I looked and it was alot of blood. I went and saw a PA she called my Doctor and he said it was implatation bleeding. As long as there was no cramping it should be okay. A few weeks ago i had a sonogram and they saw the heartbeat and everything looked fine. I am still bleeding a day later and feeling dizzy- could this be a miscarriage and i don't know it?