Hello, sir that pimple like thing on the scrotal skin could be sebaceous cysts, in early stages they are soft (just like pimple) and can able to pop them but as time goes the oily material in cyst get hardens and difficult to pop,, they can be removed by simple excision by surgeon. And yes that burning sensation can be due to small particles of sand causing minor abrasions below your prepuce, or could be balanitis, Please consult a general surgeon for both.