Dog is Itching

Question
My dog has been continually biting at and itching the lower half of his belly. I have looked at it and there is no redness, he has no fleas, and there are no signs of a bite mark. He will suddenly sit down when walking and sometimes it gets so bad, he whimpers when he walks. I am unsure what is wrong, but he is still eating fine, wanting to play, and staying hydrated.

Answer
In cases like this there are two immediate things I would recommend.  First, I would have the dog bathed and then dipped in an insecticidal solution of either amitraz or phosmet.  Your vet can do this for you.  Then have the vet give a shot of a steroid, like dexamethasone.  If the itching goes away and does not return, then there may have been a parasite on the skin that you could not see.  If the itching goes away for a week, then returns, the steroid shot helped, but wore off.  In that case there is probably an allergic reaction to something and the dog can continue on oral steroids.