Low potassium is matter of concern as it can affect your heart, muscles etc.
You are on a diuretic for blood pressure.
Diuretics lower the potassium level by making you 'pee out' potassium.
Your doctor should change your blood pressure medication to another medication ( like lisinopril, amlodipine etc.).
You should take bananas, drink fruit juices in the meantime.
They are rich in potassium.
You may also need potassium supplements if your potassium level does not reach above 4.