What can cause a heavy pressure under my cheek bones, about at my jaw. Not painful, just lots of pressure feeling. Bend over and head feels full.

Acute sinusitis. the are behind the cheekbones are the maxillary sinuses. These can become congested from infection or allergy and can actually have a fluid buildup which when changing head position will give the feeling of fullness, pain in the upper teeth and or ear pain. While not an acute situation you should see you local MD for medications and possibly radiographs.