NO.5 I've just had a Haircut

Oh my! What did I do?! I've just had a haircut. This guy girl(1) in front of me in the mirror is so strange to me. She's not the person I knew yesterday or anytime(2). The barber cut my fringes really short. What a ugly girl in front of me in the mirror! I feel sad. I wish my hair would grow quickly so I can be myself again.
This is a just short diary. But it's involved contains(3) all my feelings.

(1) "Guy" refers to males. You use "girl" in the 7th sentence, so maybe you knew that already!

(2) "Yesterday" used in that way doesn't just mean the day before today. It means "yesterday or any other time." It's something people say when they are thinking about the past sometimes.

(3) If you say "contains all my feelings," that means you put all your feelings into it. I think this is what you were trying to say.

Human hair grows at an average rate of 1.25cm per month - don't worry :-)

NO.5 I've just had Hair Cut

Oh my! What did I do?! I've just had my hair cut. This girl in front of me in the mirror is so strange to me. She's not the person I knew yesterday or ever. The barber cut my fringe (American English: bangs) really short. What an ugly girl in front of me is in the mirror! I feel sad. I wish my hair would grow quickly so I could be myself again. 

This is a just short diary, but it covers all my feelings.

"Guy" is masculine. We do use "guys" in the plural to refer to groups of men and women, but the singular always refers to a man or boy.