Hi and welcome to the Forum! I took the liberty of moving your post from Intros to the Tomato section, since it was a tomato question. The Intro section is really just for saying hi and telling us a little bit about yourself and not every one takes the time to read it. More people will see it here that might be able to answer your question.
Your picture didn't come through. I don't know what you were trying to do, but it looks like an email address in there. You can't post email. Pictures have to be hosted on line somewhere (like photobucket) and then can be posted from there to here. Instructions are linked in my signature line.
But without a photo, just from your description, sounds like it might be blossom end rot. Is the rotting area at the bottom, opposite from where the tomato attaches to the stem? Does it look something like this:
If so there's a Sticky about blossom end rot at the top of this Forum and/or you can type blossom end rot into the Search the Forum Keyword box and find tons of info about it.
If you don't think this is it, try again to post your picture.