It must be frustrating to be having these itchy rashes for 3 weeks. PUPPP often occurs in the third trimester of pregnancy and improves on delivery, although I have seen some people develop this condition after delivery.
To be more certain about the diagosis of your skin condition, you might want to consider visiting your dermatologist.
Dermatologists specialize in the diagnosis and treatment of skin disorders and will be able to assess your condition and advise you on the appropriate treatment and management.