Well, I'm no Doctor and I certainly can't diagnose for you, but if the dark spot is rather purplish and looks like a bruise, then it could be internal bleeding/hemorrhaging cause by your stomach. Go see a doctor ASAP, for I'm not...
I don't know what it could be from, but skin spots can normally be signs of cancer
you might want to go get it checked out
are you over weight skin darking could be from the skin covering skin ask any large breasted women im a dd and under mine its dark
It would be a good idea to see a dermatologist.
They may decide to do a biopsy, if the spot looks suspicious. This involves local anesthetic and a stitch or two. No biggy.
I would not let this go without seeing a physician.