What Causes Bleeding Mid Cycle After Menstruation?

Good day. I am 19 years old. This month, i had my period from April 4-9. Well I'm not sure with the last day because I went swimming with my family last April 9 and I still had very light bleeding. I'm in the Philippines so using of tampon is not really popular here, instead we use napkin. So there. My period ended that day, usually my period lasts for 6-7 days. So yesterday, April 20, I was surprised to see light brownish bleeding in my underwear. :( I'm scared that this might not be normal. Any doctor that could help?