Why do I wake up at 3am?

Like I've said before, it could be insomnia. It could be nightmares you're having, too many things on your mind. There's a lot of different possibilities.

There was once that I woke up at 3am, I woke up finding myself not being able to move my body when my mind is entirely awake. I remembered vividly staring at the ceiling as my family were sleeping. I tried moving my limbs but it didn't turn out possible and the sleep paralysis continued for 2 to 3 hours before I start feeling bodily sensations. I remembered that I was kinda telling my body to "move, move, move". It's quite an experience I would say.

i guess its because you are used to that,

Our bodies go through repeating cycles of sleep every 90 minutes. If the issue is not wanting to wake up 3am, try adjusting your sleep schedule so that your body continues to sleep during that hour. Are you going to bed too early than you are preferring which is causing you to wake up at 3am? Are you having dreams that are causing you to wake? There could be many factors. Sleep hygiene is a vital aspect that we must care for greatly in order to stay healthy. Backtrack your sleeping habits and figure out where you can make any adjustments.