Hi. From the location you described, that lump seems to me to be a lymph node, which is normally found in that area. A one centimeter size node in that area is not unusual, and if it's not red or tender, then you may opt to just observe it for a month or two. If it grows bigger, or additional symptoms appear, then that's the time to have it checked by a doctor.
I have the same, but it is very new and is a bit sore from friction, when I walk a lot and the dampness in that area. It is not really sore to the touch otherwise. I seems to be like the small boils I had when I was young.
Did you find out what it was, did it go away, I have the same thing so just wondering what it is.