Hello from JustAnswer. This is Dr. Love, a different expert.
There is a long list of conditions that can cause mild temperature elevations. By a strict medical definition of "fever', a temperature of 99-100 is not considered a fever, although it is commonly referred to as a low grade fever, as you are doing. Once infections have been excluded as a possibility, the most common causes would be some type of chronic inflammatory condition.
Certainly, chronic inflammation related to allergies can cause this, which is why allergic rhinitis is called hay fever, and if you are having other hay fever symptoms, treating the allergies more aggressively would be appropriate.
However, it is also true that chronic inflammation of the pancreas (pancreatitis) also can cause fever.. This can be related to inflammation surrounding a tumor growing in the pancreas, but also can occur from other causes of chronic pancreatitis. If this nodule turns out to not be cancer, it could be an inflammatory nodule, and the mild temperature elevation could be related to the inflammation.
You do not say whether any pancreatic blood tests have been done, such as amylase or lipase, and if not done, these tests may indicate evidence of pancreatic inflammation.
There also can be a variety of chronic inflammatory conditions that can cause lo grade temperature elevations, so if allergies and pancreatic diseases are excluded as a cause, the next step would be evaluation to look for evidence of systemic inflammatory conditions.
If I can provide any additional information, please let me know.