If you're female between like 13-17 that's very common.
That makes sense too in a weird way. It could be when you're getting tested. Also look into possible thyroid disfunctions, they can mimic symptoms somtimes. (Same story in my family). Another thing is, well, do you eat enough? Those can all be huge signals that youre body isn't getting enough fool or the right types of fuel.
drink more water and talk to your doctor about it
I used to kinda feel like that..but now that I'm heavier...I don't sooo I don't know if it's connected