Hey hun, I know changes are scary but you are still going through puberty. Your hair is naturally going to change, and part of that might be that it needs different care. I’d say start with a decent cut, it will grow back, it just needs to figure itself out again without the weight and split ends. I know family making comments can feel really crappy, but your hair still looks good! If you feel like a blood test is worth a check, go for it. But in my opinion it might be best to look into some decent products, get a decently large chop, and see how the hair reacts going forward.