Try not to be too anxious, hopefully the scan will reassure you tomorrow.
It does happen to many women, my dr said about 30% and in most cases all is fine.
Brown blood is old blood, it can be just hormonal or as someone said above, the body clearing out.
I had spotting from 12 days past ovulation, almost constantly through till about 7 weeks and then a few brief episodes of brown spotting (not lasting more than a few hours) up until about 10 weeks.
I too was very anxious.
I really hope all is well,

Take care