Unfortunately it does sound like you have PUPPP. The cause of this rash is unknown. It usually goes away following delivery and is more common in first time mothers in the third trimester and those pregnant with multiples.
PUPPP has been renamed as PEP (the European name) so if you do some research you may find more info that way.
Here is a link to Wikipedia's page on PUPPP (http://en.wikipedia.org/wiki/Pruritic_Urticarial_Papules_...)
Some comfort measures include oatmeal baths, using a lot of gentle moisturizer, and wearing all cotton clothes to avoid irritation of the skin.
If you are concerned or the rash is driving you crazy, call your doctor and insist to be seen sooner and be taken seriously. It sounds like he blew off your concerns and how uncomfortable you are. After all, you hired him to do a job. He works for you:)