Is it bad that i feel very tired not long after waking up?

I've been having this schedule all the way back since December, when I finished high school. I'd wake up between 14:00 and 15:00, and then stay awake until between 6:00 and 8:00, and repeat it all over again.

I was supposed to start full schedule on university last month but due to the quarantine it didn't happen, and I started having online classes between 19:00 and 22:45, and I'd spend from 16:00 to 19:00 doing homework and studying.

In these last few weeks I've started experiencing tiredness not long after waking up: usually around 17:00 or 18:00, when everyone is taking a nap in my house usually (as most of them wake up between 10 and 12). I'd be sitting in my desk, listening to music and maybe doing something and I'll start falling asleep, and I'll be so tired as to fall asleep on my desk, without being actually able to fight it; all my will is gone, and I just fall asleep for up to an hour and a half or something.

This is somewhat alarming, I know my schedule is bizarre and I should change it ASAP but it's what works right now for me, but I don't think I should be feeling tired after 2 or 3 hours of being fully awake and fine. I'll just doze out into a light sleep state where I'll be semi-conscious but might still be able to have dreams.

Has anyone else experienced this?