What you have describes sounds typical of an abcessed baby tooth. When baby teeth become infected you will usually notice a little "gum boil" next to the tooth. Treatment in this situation usually is either a pulpotomy
or extraction. A pulpotomy is the removal of the infected nerve
inside the tooth. This is done to preserve the tooth assuming it has not decayed to the point that is is not restorable. If the tooth is not restorable, then the only option is to extract the infected tooth.
Hope this helps,