Happy approaching holidays. Thanks to everyone who's taken an interest or responded to this thread.

I have an update...unfortunately, not the best one, and perhaps only a partial answer. In essence, as of a few days ago, my father has been diagnosed with prostate cancer. While getting a whole range of tests for his mysterious pain, his GP noticed a high PSA score in a blood test and recommended he get a prostate MRI, which he did. These results were then passed onto his urologist, who sent him for a biopsy, the results of which, unfortunately, point to cancer.

The good news is that I understand his particular brand of prostate cancer is neither unusual, nor advanced: acenar adinocarcinoma, with a Gleason score of 7 (3+4), and a grade of 2. The bad news is that we both remain uncertain what relation, if any, this has to the pains he suffered. Again, my research suggests most prostate cancer shows no symptoms in early stages; certainly, happily, my father hasn't experienced any of the (primarily urinary) symptoms related to advanced cancer. That being the case, we're both struggling to understand how undiagnosed prostate cancer could be responsible for his multitude of mystery symptoms: abdominal pain, fatigue, and weight loss seem potentially related; head pain, chest pain, and underarm pain, less so. On the other hand, the idea that he might have something else going on simultaneously to prostate cancer is obviously worrying, especially as he looks at his treatment options and considers the best course of action.

As always, would love to hear people's thoughts, and wishing you all well.