I seem to stay awake and alert until 4 am or later; I am just not tired. But I will wake with the faintest first light of dawn, after just a few hours sleep, and exhausted all day. On a camping trip I will tend to go to sleep earlier. If I cover my windows with dark shades, I will often sleep 8 solid hours and awake refreshed through the day, but that means waking up at noon - not too convenient for the working world. I am making my housemates crazy already. What to do?
You're describing a prevalent circadian rhythm sleep disorder, the delayed-sleep phase type. An irony is that exposure to dawn light after just a few hours of sleep will wake you up, but in fact sustain or exacerbate the delayed sleep in the days following. There is a well-tested, non-drug treatment for delayed sleep phase, which begins with light exposure (a/k/a light therapy) at the end of your biological night (which may be around noon). The strategy is laid out in detail in my paperback, Reset Your Inner Clock (Penguin Random House, 2013). See also www.comprehensivechronotherapy.com for information about our clinical service.