7 year old bathroom problem

I have a 7 year old son who a few months ago started soiling his pants at home and at his grandparents houses.  I did everything I could think of to stop him, the usual talking, yelling, punishing, and prasing, but none of it seemed to work.  Finally he got much batter at home.  Then a few weeks ago I got a call from his school saying that he was having the same problem there and that it had happened more than once and that I needed to do something about it.  I have been taking him to a child psychologist for a couple months now but the problem seems to be getting worse and his doctor doesn't know what else to do.  Then I found that my son was not going in his pants at my in-laws house but putting his fingers up there and then smelling and licking it.  I don't know what to do, I've taken him to his pediatrican and we can find nothing wrong with him, the schools and doctors have done MANY tests on him and have found only that his IQ is 112 and that he needs just alittle help to stay focused.  I don't know what to do I'm so frustrated and don't know where to turn.  Is he just being lazy or is it my fault that he is doing this.