Hello,
I cannot confirm anything without examination but it can be heat rash, eczema, sweat dermatitis, hives or scabies(is characterized by intense itching, usually at night and by small insect-type bites lesions on the skin. Diagnosis of scabies is made by scraping the skin and viewing the material under a microscope to see the characteristic mite or eggs).
I suggest you to get it evaluated from a dermatologist to confirm the diagnosis.
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 dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I also forgot to mention that sweating and taking a shower only makes it a lot worse!