What Causes Spotting Between Periods?

I am 27, 155 lbs and 5'7. I am having spotting between my period cycle for the first time ever. I have been stressed as of recently and I don't have any pain associated with this. The spotting only occurs when I wipe. It is mucus-like and pink. If I put a tampon in for a short while I won't have any for the rest of the day. This has been going of for a week now. I am not due for my period until around the 10th of the month.