As you have already mentioned in your question, it is quite classic for sinus pressure headaches to get worse when bending over, or to experience a 'sloshing' sensation with this movement from the liquid in the sinuses moving forward with gravity. The pain with the sinus headache will be either in the cheekbones or in the middle of the forehead and other symptoms would include stuffy nose or cold symptoms and cough.
On the other hand, if the pain is not in these locations or not associated with these other symptoms, then it is less likely to be a sinus headache. Other possibilities would include migraine
or tension headache, the most common types of headache. If regular pain relievers are not helping you might want to see your doctor
to determine if additional treatment is needed.
Rarely, headache in someone your age is a sign of a more serious problem. If you experience any concerning symptoms you should report these immediately to your doctor. These concerning symptoms would include dizziness, difficulty walking or uncoordinated movements, severe nausea and vomiting, blurred vision, or any numbness, tingling, weakness or other strange sensations.
As always your best source for health care information is your primary care doctor