Recurrent fatigue is a tough one to figure out. As Thomas mentions, it can be associated with a variety of different conditions, some pathologic, most not. For example, it could very likely be unrelated to your mild anemia–perhaps this anemia has even distracted some medical professionals in the past from exploring other more subtle causes.
I believe the episodic nature of the fatigue you describe may be the key to figuring it out over time. This sounds like a pain in the butt, but keeping a journal of your diet, fatigue, sleep, stress, thoughts, and training levels may allow you to associate certain training volumes, intensities, foods, stressors, seasons, etc. with when these episodes of fatigue occur. Then you could hone down on possible associations and explore them with the appropriate professional (like a dietitian if you think it may be diet related, or a coach if it’s training related). And when one lead doesn’t pan out, try a different one. You may have already done all of the above, or some of it in part.
It appears that you have monitored all your blood tests and there doesn’t seem to be any significant deficits. As Thomas alluded to there can be mild, non-pathological changes to some blood tests with heavy training, including thyroid function. I’m not sure if you’re in America, but if you are, the medical system is unfortunately not really set up for such a holistic, activity-related evaluation that you may be looking for. There are probably some healthcare professionals that do this, but they may be hard to find.
I understand I haven’t given much concrete advice, but I do wish you well in figuring out what can be quite a perplexing issue. At least it seems it hasn’t prevented you from being very active during your life thus far. And thank you for your military service. I always wanted to be military pilot when I was young but got rejected, in part, because I had a color deficiency in red.