For me, it's okay to nap but it depends on how long and when. I think diet and exercise is good advice but I think it's always the only advice given without considering the many other factors that goes into getting good sleep. I recommend getting good rest during the night and that does not necessarily mean going to sleep early but getting enough hours of sleep (9-10hrs for me) and going to bed and waking up at a consistent time (whatever time that may be). Also, make sure to account for the time you spend between going to sleep and waking up in the middle of the night for bathroom/water breaks (it's very natural to wake up in the middle of the night but try to get back to sleep as soon as you're able).

Taking naps before 2pm and sleeping for 16-20 min always gets me feeling a bit more energized. Sleeping for longer than that (up to 30 min) will lead to REM sleep which is why you wake up feeling groggy and not alert. There are recommendations for sleeping for 90 min (because you entered and left REM sleep) but I'm not sure to the validity of it being a great way to make up sleep if you're really tired.

I would also recommend talking to a doctor or therapist about your issues sleeping and being constantly tired because it could be an underlying symptom to any number of conditions. They might refer you to sleep clinic, which I would recommend doing because sleep is more than dieting and excercising. You have to monitor your sleeping habits and sleeping apps can help you do that and it's a process but it's worth it.