Hi there, voice.
Sure it can be sinus. I presume you mean frontal sinus area, not occipital which is nerve-related.
Allergies, infection, a cold - all can cause nasty thick mucus that can block the sinuses and give you a headache. I have chronic infection in one maxillary sinus, shows up on imaging.
Dryness can cause thickened mucus, making it hard for the cilia to remove bacteria, etc. I use generic 12-hour Mucinex to thin the mucus, also a good saline sinus wash with the squeeze-bottle, not just pouring saline through, not just a spray. A dab of AYR around the nostrils at night stops the "crusties."