I used to think it was related to caffeine or work stress but cutting out drinking seems to have fixed all my sleep issues.
I'd love to try a fixed sleep schedule, but sometimes I don't get home until 2am, other times I have to get up at 7:30am.
6 hours is too little IMO. If I sleep 6 hours for more than a few days in a row, I feel like shit and need caffeine to wake up properly. Then I end up sleeping 10-12 hours on my days off to compensate (and to take a break from caffeine). It doesn't feel healthy.
So, I try to get at least 8 hours consistently. That way, I don't need caffeine at all and function just about fine.
I am fully awake and ready to go a few minutes after waking up, too. No coffee needed.
I do occasionally take an hour nap here and there, but that is also rare.
Of course, spending 12-14 hours a day facing brights screens do not help.