I'm A 20 Year Old Male. I Used To Have

I'm a 20 year old male. I used to have a really really bad sleeping schedule for a very long time. I was awake when everyone's sleeping. I used to go to sleep at like 4,5am and even 7 in the morning sometimes and wake up at like 3,4pm. I got gastritis now because I didn't do any workouts and I ate a lot of meat. Specially beef. My doctor suggested me to get some tests done when I was diagnosed with gastritis which includes Fasting blood sugar, alt and ast levels, serum lipid profile, full blood count and sgpt sgot. And all of those were on normal levels and it kind of surprised me because I'm a very lazy person and I eat so much junk food. Now I'm stressed that I can't sleep on time. I don't wanna be that guy anymore. I need to sleep at 10 and wake up at 7. So I can eat all the three meals and do some productive things and some small exercises so it's benefiting my overall health. I go to bed at 10pm now and I'm just awake till the morning to get out of my bed and eat my breakfast so I can sleep because I'm adapted to that very bad schedule. How can I reset this?

My gastritis is getting better now but when it was at it's peak I couldn't sleep one second. My stress and anxiety levels were through the roof. I really tried to sleep at daytime but it's too hard for me to fall asleep. Even if I fell asleep I wake up again after like 2hours. But I feel like I've been sleeping for a long time and that stressed me even more. My appetite is getting better too so now I'm not that stressed. My doctor gave me atrest 0.25mg but that doesn't help me sleep at night. But my stress levels are becoming okay. I really wanna sleep like a normal person would sleep. What can I do to sleep at 10 and wake up at 7?

What if I keep being awake at my daytime which is very very hard and doing some really small exercises in the evening like pace walking to burn some calories? After getting my lunch at like 1.30,2pm I feel sleepy so I sleep at that time. So I really wanna sleep at that time. Today I felt so sleepy and went to bed at like 12.30 and got up at 2 to eat. Then I went back to sleep at like 4.45 and woke up at 7.33. This sleeping thing is killing me right now what's the best thing to do? Please please please help me I'm so desperate. I thinking I'd die without getting enough sleep. Sleep is so important for my overall health. How can I sleep and wake up like a normal person?