I have mildly low sodium blood levels. my random urine sodium is 80 mmol/l. urine osmolality is normal. my symptoms are bad muscle cramping, thirst, and frequent urination. im not on any medications and i eat a normal diet. could this be siadh?

You should let us know you serum Na, urine osmolality and serum osmolatity (measured, not calculated). For a healthy young individual, urine osmolality should be quite diluted, i.e. less than 100 when serum sodium is low. Hyponatremia may present is patient with chronic kidney disease due to the impaired capacity of diluting the urine. If kidney function is normal, SIADH is likely the culprit.