I would be totally upset that your dr didn't investigate more!!! I'd be looking for a new dr.
Check your bed again for bed bugs - they will leave SMALL dark spots on the corners and edges of your mattress. they USUALLY bite around the legs - but can get everywhere. If your husband has no bite marks on him - i would think it's not bed bugs..but then again - you NEVER know!!!
Go to a dermatologist and have them examine the rash.
You may have developed an allergy to something because of hormonal changes in your body from child birth (congratulations by the way!!)