On my blood tests i have low sodium just under the normal range and i have high random urine sodium level of 80 mmol/l. i get muscle cramping all over that gets worse with activity. is there any conditions or disease that cause this?

High sodium in the urine can't explain why you have a low serum sodium, i.e.hyponatremia, and your current symptoms. Hyponatremia is abnormal so the etiology needs to be identified so the cause of your cramp can be explained. When answering your question I assume you are otherwise healthy and not taking any medication. If hyponatremia is confirmed with a 2nd test, you should see a nephrologist.