What could cause bleeding between periods in a 31-year-old female?

Hi doctor,

I am a 31-year-old female, and I have bleeding between my periods. My usual bleeding cycle is 34 days. I have one son. I got a C-section seven years ago. For the past four months, I have been getting a mild little dark than usual, bleeding exactly on the 13 to 15th day after my period. It is just one time bleed mixed with white discharge on the 13th day. Again one-time blood mixed with white on the 15th day after my period. This bleeding is not throughout the day. Each time not enough to use pads. It is a very small amount. It is a little darker in color. After this, I get the same bleeding for one day that week before my actual period. I did not feel any discomfort during my five-day period. It is very normal. There is no pain or cramps, and do not have a heavy flow. This has been happening to me for the past four months, and now this month, I have felt mild injection-like sharp pain three times in ten days in the lower abdomen, exactly lower one inch right near my belly button, and pain is traveling to the top vaginal area which is two or three inches down.

I am seriously worried about this issue. Please help.

Thanks.