One possible difference could be that you had an enormous increase in your exercise when you went into basic training. Exercise is a natural anti-depressant. A lot of exercise causes the release of endorphins in the brain and enhances one's sense of well being. It sounds like some aspect of the basic training did you a tremendous amount of good. I doubt that it was enhanced sleep. At least I've never had the impression that basic training would be conducive to good sleep quality but just the opposite. The characteristics that you describe sound like you were introverted and anxious perhaps as much as anything.
On a separate note the clinical definition of depression is different than most people have a sense of. It does not necessarily mean that you feel sad all the time or cry often although these can be characteristics. Depression (in the medical definition) is a combination of characteristics that define negative feelings. These may include anger, self-doubt, pessimism. You might feel a lack of enjoyment of things. People who are depressed are less likely to engage in interactions with others.I don't know how well these characteristics may fit you or not. The medications available for the treatment of depression are a tool that can be helpful. Some people will benefit to a greater degree than others. Some people will respond to a certain class of medicine versus another. The response to this type of medicine becomes very individualized. It takes several weeks typically for a medicine to reach its maximum benefit. By about six weeks you pretty much know what a certain medicine at a certain dose is going to do for a patient. The most common medicine that is started for depression is the SSRI class. This class increases the neurotransmitter serotonin. this helps many people but others do not respond so well. Still others may give up and quit to early. treatment of depression is a gradual process. There are medicines that act more on norepinephrine and/or dopamine neurotransmitters which if you should be depressed might be of more help. Depression has a typical interference with sleep. The most common pattern of sleep disturbance due to depression is early awakening and being unable to get back to sleep.
The fatigue that you mentioned can be a symptom of depression but can be a very difficult symptom by itself to nail down the cause. People always get tired and the first question is when does the fatigue cross over from the normal into something pathologic. It is not such an easy question to answer. Here again the exercise tends to help many of the causes of fatigue and I would think may be of significant help to you.
Other characteristics that you describe sound to me that you are an introverted person. There is nothing wrong with that. Being introverted can serve you well in some respects but hurt you in others. The history of stuttering is a developmental thing that many kids grow up with and this tends to improve as you mature. It to me is somewhat suggestive of some association with anxiety. The cause and effect is hard to say. Kids whom grow up with a stutter tend to have some increase in their social anxiety. I would bet that you hate public speaking.
It sounds to me that the experience of basic training helped you. perhaps it was the exercise. Perhaps the structure and discipline helped you. It may have been that the experience boosted your self esteem. I would suggest that you look back on this experience and try to recapture at least some of the properties of this period of time. Perhaps this will help you to feel better.
I think that it might be possible that medication of some type might hold benefit for you but I recognize that you seem quite cynical at this point of this approach. Certainly I'm not suggesting that you retry what did not help in the past. It sounds that you have had a good thorough work up to search for medical factors which might cause fatigue and brain fog. It would possibly help your sense of energy to take a vitamin B complex and CoQ10.(The latter is a supplement that is over the counter and is a substance that is related our bodies use of energy) The B vitamins are also related to our bodies use of energy. These supplements plus a more vigorous exercise program may help with the fatigue.
I hope this helps you out somewhat. If you have further questions or points of discussion then I'll be glad to get back with you. Good Luck to You,
Anthony Bray MD