Why do I have so much difficulty waking up at 10am, compared to timings like 7am?

I’ve been having lots of trouble / difficulty with waking up on time to go to work by public transport. On a nightly basis I usually fall asleep around 2–3am, sometimes earlier, sometimes later. I’m able to get up way more easily for morning shifts for work at around 6:45–7am, and most times feel more awake than if I sleep for more hours.

However, it’s really really difficult to wake up early enough for my afternoon work shifts — to reach on time for my afternoon shifts, I need to start getting up at 10am, leave the house before 11am. No matter how much I sleep per night, it feels impossible to get up. I feel so much more lethargic and my brain feels muddy. I barely hear my alarm. I don’t hear people when they try to wake me up, and when they touch me to wake me up, I fall back asleep within seconds. My alarm / family members try to wake me up from 9:45am onwards, and I still only manage to wake up late at 11+am and end up having to shell out money to take a cab to work twice a week.

I’ve really tried to sleep earlier and have pushed my sleeping time from 4–5am to a few hours earlier. Tried improving my sleep hygiene. I’m just always extremely tired and my body always feels heavy, and it’s worse on days where I work afternoons. On days that I do work mornings, I already get floaty by the end of my 8 hour shift and feel like collapsing, and nod off on my way home — when I get home I end up napping and can sleep till night time, shower, then fall back asleep again.

It’s been 4 months since I’ve converted to a full time role in this job, and managing the exhaustion no matter how much I sleep during my free time is like shovelling effort into an bottomless black hole. I do take some medications (my primary antidepressant being an SNRI) to help with my depression and ptsd, and have only managed to function at a reasonable level at the highest dose, even though I feel bone tired and sleepy constantly. I’m just quite desperate to stop feeling this exhausted even despite sleeping more hours and waking up in the afternoon.

I don’t understand what’s happening in my body and why sleeping longer makes it even harder to wake up, even more confused, even more running on fumes, than when I have to wake up early morning? What can I do or eat (like a supplement, med, etc.) to help me wake up and stay up more easily?

Please help 😞🙏🏻