I agree with everything the previous two posters said, but will throw out another possibility that could be contributing. At what point did you start to notice that your hair was straight? Is it straight through the whole length or is there more wave near your roots? You don't indicate your age, but you mention that you had 2c/3a hair as a kid. If you went through puberty (or any other major hormone swings like pregnancy or thyroid issues) this can also impact wave pattern, and if you were straightening your hair through all of it, it might be something that you didn't notice. Heat damage is a much more likely answer, but I did want to mention this also.

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