A pancreatic cyst can certainly cause epigastric pain radiating to the back if it is associated with pancreatitis. However, an isolated pancreatic cyst may just be an incidental finding. Your GP should be able to inform you if you should be concerned about the cyst.
A D-dimer test measures the amount of fibrin (protein found in blood clots) byproducts in the blood. The test is ordered if there is a high suspicion of blood clots such as chest pain, leg pain, rapid heart rate, etc. D-dimers are screening tests and it must be emphasized that a positive test result is NOT DIAGNOSTIC for a blood clot. In fact, many other conditions can result in elevated D-dimers such as infections, inflammation, heart disease, or recent trauma. In your case, the d-dimer may have been elevated by pancreatic inflammation but it is difficult to say as the cyst may just be incidental.
The best test to rule out a blood clot in the lung is the CT Angiogram (which it appears you had). A negative result rules out a blood clot in the lung. With your CT scan being negative, it is highly unlikely that you have a blood clot in your lung.
