definitely sounds like a lack of sleep. most people underestimate how long it takes to fully catch up on sleep. they sleep well for a few days, still feel tired, and rant about how they slept more and it made them feel even more tired.
take the most you can sleep at once, like if you were very comfortable and there was no alarm set, how long could you sleep? subtract that from when you need to get up, and then subtract an extra 30 mins to give you time to fall asleep and for a little cushion in case you sleep longer. that's the time you should be in bed the day before, trying to fall asleep. start winding down the hour previous to that. don't have any caffeine past breakfast
for example, you can sleep 9 hours at most. you have to wake up at 5am to run before work. to wake up at 5am without an alarm, you want to fall asleep by 8pm. start winding down at 6:30pm (no more carbs, no stimulating activity). be in bed with lights off at 7:30pm.
do that routine every day (yes, even on weekends, keep the same sleep schedule) for a few months. the amount you sleep will probably gradually go down as you get caught up, so if you can sleep 9-10 hours now don't freak out like you gotta sleep 10 hours the rest of your life. you may go all the way down to 7 once you're caught up, but that could take over a month.
if you are still getting tired midday after good sleep hygiene for a few months, i'd be quite surprised