What Causes Brown Vaginal Discharge?

Hello, I was wondering if you could help me. I finished my period on the 2nd of this month (september) but for the past few days I have been getting a brown/reddish discharge. It's not enough to fill a pant-liner but it is worrying me. This happened 2 months ago too but my last period was fine. I have recently travelled from the U.K. to Japan and my diet has changed considerably. Could this have anything to do with it?