Why is my hair unevenly curly?

My hair is unevenly curly, it's a type 2b-2c waves/curls at the back of my head but the hair on the front of my head and and the top of it are almost stick straight. When my hair is wet it's almost all have the same texture but ones it dries it gets all uneven. I used to always straighten my hair because of it but i've been straightening it for over three years now and I'm sick of it ! I tried some styling products but none of it works. (The hair that is straight is also VERY thick and even when i curl the hair the curl tends to weight down and end up not staying in the hair for even half of the day) HELP!!

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