I had bright red spotting bleeding, brown spotting and pink spotting on and off throughout my entire pregnancies with both of my two healthy boys. After numerous early ultrasounds, blood tests, etc. no one really could figure out why as everything always looked perfect in my uterus. It's really hard to know anything definitive on u/s before 6 weeks or before a baby/heartbeat can be seen so its kind of a waiting game. The doctor thought for me, it was my likely cervix being sensitive as there is more blood flow and vessels burst easier I guess.
I'm 5 weeks right now and haven't had any spotting with this pregnancy so far, but I'm just waiting for it to start. It seems to be the rule, rather than the exception for me. It's definitely nerve wracking, that's for sure. I'm not saying its normal, or there's nothing to worry about but these things do turn out ok sometimes!
I know it's scary and so frustrating not knowing what's going on but try not to panic!
Best of luck to you!