I live in Cherokee, NC. I have Cherokee Purple tomatoes and Big Boys. They grow and then before they are ripe, they have rotten spots in them.
My Tomatoes Grow but They Have Rotten Spots Before Ripe
Certified GKH Gardening Expert
It does sound like you may have some blossom end rot. Here is more information: https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossom-rot.htm
If you are talking about a black spot on the bottom (?) of the tomato it could be blossom end rot - very common when the plant doesn't get enough calcium. Also, check your tomatoes for little insect holes - I'm an "organic" gardener - no pesticides for me but there is the inevitable downside. Hope this is helpful