이거 ''진짜'' 다야몬드야.---> This is a ''real'' diamond.(informal) 

저 여자 ''진짜 or 정말'' 예쁘다.----->That girl is ''really'' pretty.(informal)

--> If you want to use "정말", Generally you must use "정말" about people.

     For example, that man is really nice - "저 남자는 정말 멋있다 or 저 남자는 진짜 멋있다."


''아이고'' !! 참나.---->Omg!! unbelievable.

-->"아이고".. this word is not mistake. But in Korea it is used by elerly man and woman. There is a lot of words in these case. I think "진짜?!!" or "정말?!!" is good expression in here. 

-->"참나" no. Unbelievable is "믿을수없어! or 믿기지않아!"

--> As a result, "정말?! 믿을수없어."

''아이고''!! 어깨가 계속 쑤시네.--->Omg!! my shoulders are continuously aching.

-->"어깨가 계속 쑤시네." is quiet good. But this is also used by elerly man a woman. The better expression is just "어깨가 계속 아파."

''아이고'' 괜 찮 어?--->Omg !! are you okay?

-->"괜찮어? or 괜찮아?" anything is okay.