Spotting for no reason

Amanda
I am 13 weeks 5 days. Had a check up last week both had heartbeats of 158 and 163. Every 4-6 weeks I have some spotting. The doctor keeps telling me as long as I don't have pain and it doesn't fill a pad or last longer than 2 days not to be concerned. They can't find anything on a scan that says why this may be occurring. Have any of you gone through this?