11-12 is not an optimal time for sleep. It's also not good if you're using electronic devices while you try to sleep (blue light disturbs sleep and activates the brain). It's better to reduce the amount of stimulation you experience by powering off/silencing devices, shutting off the lights and maybe using a white noise machine (fans also work great for this). Taking a warm bath can also help relax the body by easing muscle and joint tension.
When you wake up and feel tired during the day, it's also acceptable to take intermittent naps (try to set alarms so you don't nap longer than 1 hour at most!!!), as they will actually help you reduce your sleepiness and will give you more energy. Make sure to stay hydrated and as said in one of the posts above avoid caffeine and other stimulants that can wire you up.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this
as a student with a pretty busy life schedule i sympathise with this entirely, having survived on 3-4 hours sleep for weeks if not months on end last year during exam crunches and whatnot, but eventually you learn a primary motivation to screw everything on right - it makes you ill, simple as that. usually the negative consequences, both physically and mentally, are enough but sometimes it can take a while for you to want to fix it (as it did for me)
if you
must insist on using a phone or w/e during bedtime, use the Night Light feature and put it on the warmest temp setting possible; i have mine scheduled for 9PM (everything from phone to PC) and by god even though it's a small difference it has had a HUGE impact on my sleep hygiene. as Satricial said, using some kind of ambient noise generation like a fan or even something from Spotify like a rain/storm playlist can always help with sleeping; calm music is usually sufficient for me though
only recently have i properly fixed my sleeping pattern after spending 2018 with the most horrible pattern simaginable (think waking up at midnight and then sleeping at 4-5pm for a month straight) and it definitely took some time but i usually sleep around 22:30-23:30 right through til 7-8am. i do try not to nap so i don't ruin my sleep at night but power-naps are perfectly acceptable
i used to neck 2 cans of redbull (250ml each) for like 6-7 months straight as well and that ruined my body for a good while so please avoid that xx
try your best to stay awake when you're falling asleep and sleep at around 10pm
i guarantee that will fix your sleeping schedule
this too