I think you should be asking your Dr that question. Call ASAP and find out. Good luck to you
i too had heavy bleeding and later brown spotting in my first pregnancy,in my case it was due to subchorionic hematoma (u can call it collection of blood or blood clot),As per my understanding this could be the reason of bleeding in your case as well.Though Doc is the best person to tell you but m sharing what i know as per my experience,
These blood clots are not very uncommon and can cause some really heavy bleeding episodes along with spotting,but in most of cases they go on their own by week 12-15 or maximum by week 20.
They may be scary due to bleeding part but they dont cause pain and normally do not harm the baby and you continue to have a healthy pregnancy.
They can be detected by scan and Doctors keep a track of the size of blood clot by regular scan. If it is decreasing its good.
I hope it helps and In case you want to know more you can inbox me also.