Проверьте на ошибки в грамматике : 1) i'm underweight. it might be a good idea to add more food with protein in your diet. that's not a bad idea. 2) lack of concentration disturbs me in study. you might feel better, if you go to bed earlier and start to do physical exercises. thanks. i will try it.

1) I'm underweight. -  It might be a good idea for you to add more food with protein to your diet. - That's not a bad idea.
2) The lack of concentration during my studies concerns me. - You might feel better, if you go to bed earlier and start doing physical exercises. - Thanks. I will try it.