Eczema Treatment Care

my 4 month old has a bunch of dry skin patches all over, he has two patches on his arm that are like dry and scaly & gross. My pediatrician told me it was soborreic dermatitis. My cousin just told me she came in contact with scabies and that i should take aiden back to the doctor to find out if thats what it is.
my ped told me to use hydrocorizone cream1% everyday once a day to treat the seborric dermatitis, when i forget a dose the rash comes back. If i were to use hydrocorizone cream on scabies would it go away and come back like this? or am i freaking myself out?

I woke up Friday morning with a few blisters on each wrist. Throughout Friday the rash spread to my leg then abdomen. By Saturday it had gotten worse so my family made me go to the ER. The ER doctors said it was maybe contact dermatitis or a virus. They gave me a shot, prednisone and stuff to help the itching. It hadn’t gotten better by Monday but in fact had spread to my toes so I went to my doctor’s office. My doctor couldn’t see me so a nurse saw me, freaked out and sent me to a dermatologist. The dermatologist said she thought it was a drug allergy. I take a few medications for my headaches and back problems. She kept saying, “it’s so diffuse that it has to be a drug allergy”. It hasn’t gotten better and I was googling, accidentally came across scabies and it looks like my rash. Now I am freaking out!!!!! I don’t want to give this to my baby. Could my doctor miss scabies? I have dogs. I have read that dogs can pass it to humans and have also read that they cannot. We have had all of these squirrels dying in our neighborhood, is there a link? I can’t possibly think of where else I could have gotten scabies. I also really want to know; does scabies spread that fast over your body?