Is there anyway that it could be a brown recluse bite. I was looking at that and the signs seem to fit how he is feeling.
Welcome to the MedHelp forum!
From the picture it looks more like a bruise or a healing injury. Please confirm that it is a bruise or not.
The various possible reasons for a bruise are low platelet count, clotting disorders, fragile spider veins, deep vein thrombus, deficiency of Vitamin B12, folic acid, or Vit K, a liver disease or certain cancers. It could also be due to pressure urticaria.
The other possibility is a mole that has become red. This could be due to infection or cancer. It is difficult to comment without actually examining. Please consult another doctor if possible or provide more details—what it looks like, how it happened etc.
Hope this helps. Take care!
http://s136.photobucket.com/albums/q176/mikenash_01/?action=view¤t=bite.jpg
http://i136.photobucket.com/albums/q176/mikenash_01/bite.jpg
wasnt real sure which link would work