Is it normal that i don't know the reason?

You dont have self actualization. Go find yourself.

Other possibilities:
You may have done something stupid/outrageous in the pass that you cant get off your head.

You are trying your best to "avoid failure" and not achieve success.

You hate your parents or dont stand up to your parents enough.

The bullying really affected you a lot.

Suggestions:
Try Brazilian Jiu-Jitsu
-It is proven to help people find themselves.
-Its great exercise(will help you increase your self confidence and self esteem)
-You get so tired after the classes that you have no time to think about feeling lonely or depressed but fall straight into relaxing sleep.
-I lost 60lbs
-Its engaging because your kinda fighting someone, and your testosterone will be released making you pushing yourself as far as you can go.(pushing your limits all the time)
-It will relieve you of your fear or traces of being bullied.
-Its a low-risk sport with high rewards
-just the thought of being able to submit a guy bigger than you through simple technique is awesome enough.

I was the same exact person. word for word.

Oh there's a reason for everything. You not knowing why, doesn't mean there's no answer to be found. You can find it, you just gotta search places in yourself that you have yet to search. Maybe there's a pattern you don't see about your life. Ask someone who would be able to tell you.

Its normal to feel frustrated and depressed; especially when your young and trying to find shit out about yourself.
Feeling like being violent and actually being violent are 2 very different things. It is normal to fantasize about things you know you will never actually do.
You have to let go of the things that happened to you in the past - let go of the hope that it could have been any different.

I get bullied all the time but i dont let it get to me, they can say what they want it does not phase me if they dont like me they can go fuck themselves

Well...why are you feeling that way? Do you have depression/anxiety? Maybe you should talk to your doctor; you may need some meds. Also you mentioned you used to be bullied. Even though it was a few years ago, you still may not be completely over it. My advice is don't worry. People can be mean. I guess they had nothing better to do with their time than hate on others for being who they are. It's not your problem.

My best advice would be to calm down. Stop over thinking things, ya know ? Just tell yourself that whatever happens, happens.

Horones! Try herbal Kalms tablets.