Long story short, I've been at least semi-nocturnal for the vast majority of the past decade. I've worked third and second-shift jobs, as have people I've lived with, and my natural inclination just seems to be toward being a "night owl" as it is. But even with all of that, my sleep schedule has gotten so out of whack thanks to being unable to sleep at night in the morning that for the past few months, I've been staying up til around 6-7am.
I don't often sleep well, between just waking up for no apparent reason, having trouble getting to sleep in the first place, and being woken up by noise from my grandma, who I'm currently staying with. I don't have anywhere else I can stay at the moment, unless I were to drop money I can't really afford to lose on a hotel for a few nights just to see if being in a quieter environment would help.
But now that I've left my second-shift job, I need to move back to a more daytime-oriented schedule so I can get a new job and get things done in the meantime. I don't know what my next job's schedule will be, but I don't plan on applying for any more night shift jobs because that schedule has already done a number on my health. I also have a lot of things I need to do, including getting my car inspected (which I only have one week to do, as I've had to put it off so far thanks to work and health problems and now sleep issues).
I've tried everything. Setting alarms to get up early (thus getting less sleep) just leads to me being too tired to get out of bed. Staying up all day to be more tired at night just leads to me getting a "second wind" and staying up even later, then having it all hit me like a freight train in the middle of the following day, ruining my schedule even further. Moving my bedtime back a little each day would be ideal if not for the grandma factor. I can't go to bed at 6 if that's when she's getting up and making the most noise. And yes, I've tried all manner of things to drown out the noise, but nothing I can do is loud enough to cover up her noise--and if it is, then it's too loud for me to sleep. Earplugs just plain don't work at all, and sleeping in headphones is so uncomfortable that it just creates a whole new reason for me to constantly wake up or not be able to fall asleep, even if they mask the noise.
I am at my wit's end, here. So if you have any suggestions for things I haven't tried, or ways to improve the things I have tried, please let me know. If you've ever had to drastically change your sleep schedule in a short amount of time, how did you do it?

Well I was going to try staying up one last time, but I thought better of it because I cannot trust myself not to end up napping during the day, which just defeats the whole purpose. Unless I'm kept out of the house, which I don't have anything to do so on a Saturday, I will inevitably end up falling asleep at some point.
So I managed to go to bed about an hour and a half earlier tonight, solely because my grandma doesn't wake up as early on weekends, so she wasn't up before I went to bed. She did get up shortly afterward, though, and of course keep me awake for an extra half hour, but I managed to fall asleep before 7am for the first time in weeks, so that's something I guess. I didn't sleep super well and woke up at 1:30 but wasn't actually awake enough to get out of bed until 2. I haven't exactly been brimming with energy all day, either, but it's progress of some kind.

As for melatonin, I have yet to really hear from anyone I know who's used it that it has had any effect. I don't think it would do much in a situation where the main problem is someone making a ton of noise, either, so I'm iffy about spending my money on something like that.