I had brown spotting, red bleeding and some small clots with both my two boys until about 20 weeks. I thought for sure I had miscarried but after several ultrasounds and lots if waiting and worrying, everything was just fine. A cause was never pinpointed but the doctor suspected my cervix was just very friable and bled easily.
All the being said, it's impossible to say things will be fine. I understand your worry, and that's completely normal! This pregnancy, I haven't had a drop if spotting so far and I'm STILL worried. LOL. I think it's only natural. I don't think you should panic at this point. These things do turn out perfectly fine all the time!