My hair is naturally curly and thickthick and curly.

Although getting a perm to straighten it might help, I've never been motivated enough to go through with it.

Right now, I have a simple pixie cut, and to keep it from sticking up, I need to use hair oigel when I wake up.

When I was in high school, every girl had long hair, so I did I., too.

But I wasn't good at styling it, so looking back at my old pictures, I looked like a Hungarian sheepdog.

When I was a teenager, I had always wanted to have pixie hair, but I never founhad the courage to make such a drastic change.

Only aAfter I graduated from high school did, I finally decide to cut my hair, and. I've maintained that hairstyle up until now.

I don't know why, but it doesn't feel like me if I'm not in don’t have a pixie cut.

Although getting a perm to straighten it might [help], I've never been motivated enough to go through with it.

“Help” implies that there’s something inherently wrong with curly, thick hair. Many people feel otherwise. :-)

Right now, I have a simple pixie cut, and to keep it from sticking up, I need to use hair oil [when I wake up | each morning].

When I was in high school, every girl had long hair, [and so did I | including me | myself included].

I’m tempted to change “so did I” to “as did I,” but I’m afraid it might not sound quite right. Sometimes it’s hard to be certain…. 🤷‍♂️

When I was in high school, every girl had long hair, and so did I.

I couldan't imagine going back to long hair again.

I don't know why, but itI doesn't feel like meyself if I'm not in a pixie cut.

"I don't feel like myself" is a common set phrase. "It doesn't feel like me" doesn't sound natural in this context.

When I was in high school, every girl had long hair, and so did I.

When I was a teenager, I had always wanted to have pixie hair, but I never found the courage to make such a drastic change.

"Wanted" already indicates the tense you are trying to indicate with "had". Technically it does make sense, but it makes the sentence a more clunky than it needs to be.

I couldan't imagine going back to long hair again.

"Couldn't" does make sense for this sentence, however you indicated from previous sentences that it is a feeling which is present to you now. Couldn't still does make sense, but "cant" is a far better alternative. Can't suggests you cannot think of this action in the present, but couldnt suggests you can't in the future.

I don't know why, but itI doesn't feel like me if I'm not inyself if I dont have a pixie cut.

Very close, but the way you said "me" doesnt really exist. You can use i dont feel like me when...... (but this is more informal) and since you are talking about an attribute of yourself it needs to be "myself". You were close to the sentence structure if your use of "me" was correct but using "myself" means you have to change the sentence structure.