Please tell me this is pretty common...

Had an ultrasound last week on Wednesday, the radiologist said everything was good was measuring right on time and had a healthy fetal heart rate of 170. Just got a call from my dr and she said they saw a little bleed in my uterus where it was tryin to implant... I'm so incredibly confused. Also, I've read things that say it could end bad and things that say it's perfectly normal. I've tried callin my nurse for better explanation but I haven't got an answer or call back. This is our rainbow baby and I want nothin but all to be ok (obviously). My dr said it wasn't unheard of and if I start spotting it's normal but if somethin could possibly happen because of it id rather be aware that it could instead of thinkin everything is goin to be    a-ok!