First of all, the pain you are describing is associated with localized tenderness of the scalp itself. While the sinuses may cause the sensation of pain felt in other locations, it will not cause tenderness to touch in those same locations. In other words, the pain from a sinus infection may be felt in the upper teeth, but if you tapped on the upper teeth it should not cause increased pain. This is one means of differentiating pain originating in the tooth itself from that originating in the sinuses. If the pain and tenderness in the scalp which you have described is not associated with an obvious dermatological condition, then the next most likely cause would be a local problem with nerve endings such as a neuropathy.
Neuropathies can occur due to viral infections of the nerves themselves.
An important consideration in an immunocompromised individual would be a herpes zoster infection which typically causes severe pain in the skin in the area supplied by the infected nerve. OFCN is not engaged in the rendering of professional medical services. The information contained on this system or any other OFCN system should not supplant individual professional consultation. It is offered exclusively as a community education service. Advice on individual problems must be obtained directly from a professional.