Spotting

So I am 9 weeks today, I have had a very small amount of brown spotting for a few days off and on(anywhere from a dot on my underwear to just a tiny bit when I wipe). I have called my doctor and they said since they had seen a small collection on my ultrasound it was probably just implantation bleeding that never came out that my body is now passing. I'm not really having any cramps, just a little lower back pain today (not sure of its how I slept or what). I was jw has anyone else had this and everything be okay? I know they say as long as it doesn't get heavy and turn red I'm good. Just looking for some advice/reassurance. This is my first baby.