Its become too hard to concentrate with full mind.. I tried sleep and all the things which I was advise like nutrition,exercise etc but distracted thoughts won't stop like past memories while I try to concentrate on a single thing like reading etc... any medication?

Nope

What are these distracting thoughts? How long have they distracted you? Is there a reason you have not consulted a physician?

Is it just thoughts that get you side tracked, or forgetfulness and moving to other ideas. Are there other health issues.

Are you sleeping well ? Proper diet ?

Forgetfulness and lots of time requirement occur because of lack of concentration..

Its like automatic generated un-relevant(not related to subject I need to focus) thoughts are continuously created in mind while I learn something and those thoughts also get learned with the subject I tried to learn and got dreadfull worst even when focusing on difficult task.. this thing for sure effected my grades etc...

No other health problem I am having...

I would find a therapist. They'll teach you how to train your mind to calm down and how you can ride those thoughts through. There could be medications but I don't even know enough to know what I don't know about them.

I say find a therapist because it did a world of good for me. I had issues focusing, I still do, but a lot of memories of previous failures would jump into my mind and distract me. It wouldn't be the memory of the event but the feelings, shame, and embarrassment of them that would haunt me. Talking to a therapist gave me a few tools to deal with all this and be more focused. Being a student you should have some resources that you can draw on for this.

Good luck.

If your past memories are traumatic, then you need therapy. Give us a hint of what they are (without details) and we might be able to give you better advice.

Some trauma fits under PTSD, with flashbacks and sudden increase in blood pressure. You literally relive the memory. There is evidence that high blood pressure medication taken just before you feel an attack coming on helps, but this is not something you do without your doctor.

Dwelling on memories that aren't that kind of traumatic but which keep you from getting through most days also need therapy.

Have you thought about trying meditation? It's a guarantee way to quiet your mind for a bit. You can find guided meditation videos free online, or you can just sit in a quiet room, or with some light background noise and focus all your attention on your breathing. As little as one minute a day will start to improve your concentration.