Suggest Treatment For Severe Itchy Rashes On Arms And Legs

Question: 5-6 days ago I developed a terrible itchy skin rash that is mostly on my legs and arms. It looks and feels like tiny mosquito bites but hundreds of them especially on my legs around my knees and arms. The rash first developed while i was sleeping at night and the next morning i noticed it along with itchy eyes, itchy nose, face etc. pretty much EVERYTHING IS ITCHY. But the rash is mostly just my legs and arms. My teeth hurt for a days which usually happens when im fighting an infection and my lymph nodes are swollen. Im 30 weeks pregnant and have an 11 month old daughter. Claritin an hydrocortisone dont work. Im desperate for relief even if it means lathering on oatmeal, drinking 8 quarts of water, or taking salt water baths! I feel anxious and miserable unable to focus or complete my numerous responsibilities.
I have paoriasis but it was mostly cleared up because I go tanning to control it. Its flaring now with this allergy. Ive never had an allergy before this. The swelling and itchiness doesnt seem to subside. I went on vacation to cancun mexico between the 12th and 17th and developed the rash around the 21st. I also had diahhrea for 5-6 days when i got back from cancun but it seems to be better. The pictures are my leg and arm. The walk in clinic gen md did blood and stool tests that ill attatch. Im redoing ALL OF my laundry in fear that its the soap or softener because my rash happened while sleeping but it seems hopeless. How can i eliminate all possible causes? Why is this lasting so long and is that normal? How long before the culprit substance is gone will I see clearing? Can i take prednisone or is there another prescription available since im 30 weeks plus in my pregnancy? My skin was XXXXXXX and flawless prior to the rash. Thank you !