Hi thanks for your question.
Your having back pain
and your urine examination reveals slight proteinurea and blood along with concreations (what they mentioned as sand).Small concreations can cause haematuria(blood in urine) .Traces of proteins
are normal in urine.Take plenty of water to clear these concreations and consult a physion may prescribe you medicine for your back pain and haematuria.
Hope this answers your question.