Hello,
It can be due to unknowingly scratching the skin at night, body lice, bed bugs, allergy to fabrics, detergents, soaps or scabies bites if blisters appear. Check out your bed for any bed bugs and if the symptoms worsen then get the above mentioned possibilities ruled out from a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.