I Am Concerned About A Vaginal Discharge. It Began About

I am concerned about a vaginal discharge. It began about July 25 or 26 as a yellowish watery discharge that became frequent enough I began to use panty liners. There was no itching or burning, no sensation at all just the thin discharge. It became more viscous, like mucous in the next few days. I was sitting much more than usual as I was driving about 8-10 hours a day from July 27-31. One day it stopped but resumed in the evening. The flow became heavier and was alternately thin and watery (and darker in color) then more like mucous (and lighter yellow). Initially it reminded me the beginning of menstration with a bit of color spotting the yellow fluid. I was encouraged that the flow lessened and was no longer thick in the last 2 days. Today there is tenderness in the area (which could partly be because of wearing panty liners day and night for so long) and within the last couple of hours the color has become darker, looks like it could be blood mixed in. Not red, like old blood, brownish. I looked to see what the skin looked like and while I have looked at this area for some time it seems red though not swollen. There is now sensitivity and I am more aware when there has been a discharge ...not just because of wetness. I have been busy moving and arranging for a new job etc that I didn't realize how much time has gone by.
I am 62 and post menopausal. I am single and have not been sexually active since some time in 2007.