Not normal but it happens. It could be from sex, uti, infection, etc. I would let my ob know in the a.m. they may want to see u to find the cause. Good luck
If you had intercourse recently, it can cause spotting which happens because the cervix is sensitive during pregnancy. Is there a chance of that happening?
I'm not sure of the other causes it could be from, but what I've heard brown is old blood. BUT, I would let your doctor know about it.