Brown discharge @ 13 Weeks

Has anyone still experienced brown discharge or old blood after the first trimester. I am 13 weeks and 3 day and have experienced it every few weeks started around six weeks. It’s never bright and is never more than a few days my Dr has checked and my cervix is closed. I have read that it could be small blood vessels that just pop as the baby grows or not drinking enough that may cause it but my Dr never finds anything to explain why it’s happening.