Should I still be having a headache one month after endoscopic brow lift?

Yes I agree with your concerns.   It is unusual to have a severe headache this far out. I would suggest seeing your surgeon and having everything checked out.  Maybe this is just an unusual phenomenon of how your body is perceiving the healing process or something else may be causing this.  The answer for all of us is we do not know. In this case we check your blood pressure, all the surgical sites and think about other causes including neck issues.  Sometimes weird things happen after surgery which slowly go away, but until then you need to be followed to make sure nothing is being missed.   

I have had patients experience the. The tightness or swelling is typically the root cause.  Please consult with your surgeon about a simple lymphatic massage treatment for your scalp which may be helpful.