NOTHAPPYJAN
I'm sorry to hear that you're miserable.
Flying is exhausting at times. I have found over the years that my extended periods of tiredness are often associated with external factors.
I have been working with many people who are new to flying and funnily enough, many of them feel the way you do. If you are still in your early 20's you need to take into account that you are still growing, and this requires extra sleep.
I am a mother so forgive me if I sound too mothering, but if you eat properly, avoid large amounts of alcohol, cut back on caffeine, and get plenty of exercise, and sleep, it helps.
At first it seems hard to get yourself out of bed to do any exercise, but believe me, once you make it part of your routine you will notice a remarkable difference in your ability to cope with hard work and long days. Just a good brisk walk for at least half an hour, 4 times a week, would be a good start.
Have you seen a doctor?
Iron deficiency is common in females. If your haemoglobin levels are below par, your body has difficulty supplying oxygen to your brain and other vital organs. At altitude it is even harder.
This lack of sufficient oxygen results in feeling constantly fatigued.
If it is only the tiredness that is making you miserable, try some of the above and see if your perspective changes.
Feel free to PM me.