Hello,
It can be due to solar urticaria, sweat dermatitis, heat rash or contact dermatitis. I suggest you to consult a dermatologist and get it evaluated. Till that time, you can take some OTC oral antihistamine medications like Benadryl or Claritin and see if it helps.
For mild-moderate symptoms a weak steroid may be used (e.g. hydrocortisone as dermacort), whilst more severe cases require a higher-potency steroid (e.g. clobetasol propionate, fluocinonide).But they are available under prescription and should be taken only after consulting a dermatologist. Also use mild soaps and apply calamine lotion for soothing the skin.
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.
im not quite sure what this could be.. sounds like a side effect from the sun burn.. i would suggest seeing a dr right away as some sunburns can be very serious! next time youre out at the beach dont forget sunblock! and if its a tan youre wanting there are some sunblocks that do have a tanning agent in them! best of luck!