I can't sleep at night

In addition to what your doctor said-- no caffeine after 3 PM. If that's not enough, then try stopping caffeine at noon or even 10AM. Same thing with spicy foods.

Nothing exciting 2 hours before bedtime. So after your walk (a good habit to get into anyway ), no loud or fast music, no exciting or horror movies, and stop looking at the news. If you have a TV in your room, get it out of your room if you can.

Keep your phone out of your bedroom if you can. If you need it (for an alarm, work, etc.), then set it to vibrate and turn it over so you don't see notifications coming in. Try to stop all phone activity an hour before bedtime.

Use dark, light blocking curtains (you can get them on Amazon or have them made). If you wake up with backaches then you need a new mattress. Spend some money-- it really does make a difference. If your pillow doesn't give you enough support, replace it.

Keep your bedroom a little cooler than you might want. Shut windows to keep the noises of your city or town out as much as possible. If you need it, put on a fan or other droning sound to create white noise. In the summer, we use a fan. In the winter, we use a humidifier. They both work and of course they also have a second purpose so it works out really well.

Write down anything you need to remember, whether on paper or your phone, so you're not staying up and fretting over things like that.

Maintain a regular bedtime as well as you can. Weekends are going to be different, but during the week, set a reminder to go to bed at a specific time (say, 10PM), and set a second reminder for an hour earlier to remind yourself to start getting ready for bed (shower if you do that at night, etc.).

It personally helps me to lay out my clothes for the week but if you feel that's excessive or you don't have the room, then just lay out your clothes for the next day. Again, it's another thing you won't stew about.

I also do a kind of calming ritual. It's very basic, just thinking about things that I like. You can do something like this, or pray if you're religious. Just, it's something that is telling your brain, it's time to go to sleep.

If you do get up during the night, don't check your phone or turn on the TV. Get back into bed. But don't turn bedtime into frustration. If you can't sleep after trying for an hour, then get up-- and if it's more than an hour before you have to wake up, try calming yourself again. If you really, really can't sleep, it's okay. That happens.

Keep your bed for two purposes only: sleeping and sex. This means, don't work in bed, eat in bed, watch TV, etc. Don't associate your bed with anything but satisfaction and sleep.

I know that this is a lot, but it'll become second nature.

PS your English is great and very easy to understand.

Happy sleeping!

jespah had great suggestions - basically you need to train your brain that at night is time to sleep.

Your Dr. said it is about bad habits - exactly - jespah told you ways in which you can train your brain that night is time to sleep - follow the ones that work best for you in the sense those that you would easily and enjoy to follow. That would make it more likely you will continue to follow these.

It seems you started to do this a little bit - the problem - you did for 2 days only. Unfortunately it may take you much longer to train your brain to sleep at night. Think of it this way how long have you had this sleeping issue? It took that long for you brain to learn to not sleep at night - you need to give it more time. I think I heard it may take 2 weeks (not 100% sure) to break a habit. So you need to be persistent over a longer period of time.

Based on my personal experience with insomnia, both Jespah’s and Linkat’s suggestions are right on the money. Perhaps in your diet also you can try to lessen your intake of sweet foods. intake after 6 pm. After 2 weeks or so your wake/sleep cycle may change for the better. It did/ does work for me.

Giving these changes some time (2-4 weeks)/to take effect is a wise approach. Think about whether or not anything is making you anxious or upset (financial, schoolwork, relationships/job worries). Try to either put that aside or get counseling to help reduce the anxiety.