I've been taking sertaline for a little over a week now and every night i have a dull headache. is this normal? and how do i get rid of it?

It is not uncommon: It is not unusual to have transient dull headache for a week or 2 with ssris like sertraline. It goes away on its own. Otc headache medications may or may not help with this. If it is severe or goes beyond two weeks then a switch to a different antidepressant may be needed.

Can be a side effect: This class of medicines may cause headaches if the problem persists tell your prescribing physician.