Musculoskeletal strain: This is often the most common cause of back pain, including pressure sensations, due to strain or overuse of the muscles in the back. The location described, above the waist and underneath the ribcage, could easily be related to muscle strain from lifting, bending, or other physical activities.

Costochondritis: Inflammation of the cartilage that connects the ribs to the breastbone (sternum) can cause pain and pressure in the chest and back, especially if the inflammation affects the lower ribs.
Gallbladder disease: The gallbladder is located under the liver on the right side of the body, and problems such as gallstones or cholecystitis (inflammation of the gallbladder) can cause pain that radiates to the back, particularly under the right ribcage.
Peptic ulcer disease: Ulcers in the stomach or the first part of the small intestine (duodenum) can cause pain that is felt in the back, especially if the ulcer is located on the posterior (back) wall of the stomach or duodenum.
Kidney stones or pyelonephritis: While kidney stones often cause severe, colicky pain, they can also cause a more constant ache. Pyelonephritis (infection of the kidney) can cause flank pain that might radiate to the back.

Pulmonary embolism: Although less common, a pulmonary embolism (a blood clot in the lungs) can cause sudden, severe chest pain that might radiate to the back. This is a life-threatening condition that requires immediate medical attention.
Aortic dissection: A tear in the aorta's inner layer can cause severe, tearing chest pain that radiates to the back. This is a medical emergency.
Pancreatitis: Inflammation of the pancreas can cause severe abdominal pain that radiates to the back. The pain is often constant and may worsen after eating.

Tumor: Tumors of the spine, kidney, or other organs in the abdomen can cause back pain, though this would be less common and might be accompanied by other symptoms such as weight loss or changes in bowel habits.
Sickle cell crisis: Individuals with sickle cell disease can experience episodes of severe pain due to sickling of red blood cells, which can cause a variety of pain patterns, including back pain.
Herpes zoster (shingles): Reactivation of the varicella-zoster virus can cause a painful rash that might precede the rash by several days, potentially felt as pressure or pain in a dermatomal distribution on the back.