Low serum potassium 3.0 and low 24 hour urine potassium of 19. does this indicate not enough potassium in diet or something else?

This is serious: What to make of the 24 hour urine potassium is up to you and your physician. For potassium, you'll excrete pretty close to the same amount as you absorb through your gut -- that's basic biology. But running a low serum potassium warns of a potassium-wasting nephropathy or hyperaldosteronism -- both are fairly common and quite serious. Please continue the workup -- renin/aldosterone ratio etc.