How can I tell the difference between a blood pressure thing and something more serious for the cause of my head pains?

If HA goes away. If head ache goes away with BP improvement, it is highly likely it is from bp. If it does not improve with BP undercontrol, it is probably secondary to different cause.
What's your BP? Simple. What's your blood pressure? Is it low or normal when you are having headaches. Then it is not the cause of your headaches. Identifying and treating blood pressure is one of the most powerful facotrs for long life. Look for other factors causing headache.