Unusual Spotting Brown/Pink

I am experiencing brownish and pink discharge from CD12 onwards. Currently on CD14. My period last month was lighter than usual (only lasted 2 days with spotting one day post and prior to the period) without any cramps. (Usually high AF cramps)

On CD12 the discharge started as pink mixed with watery CM and got heavy with brown discharge. Had a sharp back pain and light cramps throughout the day.

On CD13 more pink discharge with light bits of brown.

On CD14 only pink discharge in every wipe and tad bit on the liner.

According to the app my fertile window is starting now. I have been using clearblue digital OPKs and another local brand, the result is still negative from CD10 until today.

My cycle is always constant with 30/31days.

Did anyone have a similar experience?