There are a number of possibilities. Including the possibility of a malignancy. I am not going to speculate, but you have to see a physician. Not visit a website. I don't understand the comment "I have no insurance". There are hundreds upon hundreds of free clinics in the United States where illegal aliens manage to get treated day after day for nothing. I worked in several hospitals and can assure you that this is the case. Other clinics require an interview and if you don't have much money charge a flat ten dollars a visit. There are also "Hill-Burton hospitals" which can be located with a google search on "Hill-Burton". Look for one in your area that will accept patients. This is not going to heal.
I didnt' know what to tell you so I googled it and came up with this site. Here is a qoute followed by the website which talks about wounds. Wish I could be of more help.
"Wounds with rough edges and tissue deficit (a crater) may take longer to heal. When there is a crater and the edges of a wound are not brought together (left open intentionally), bumpy granulation tissue grows from the exposed tissue. The granulation tissue is eventually covered by skin that grows over the wound from the cut edges to the center. When healing is complete, the granulation tissue develops into tough scar tissue."
Copy and paste this:
http://www.diagnose-me.com/cond/C233696.html