Hello. My Daughter Will Be Three Years Old Next Week.

Hello. My daughter will be three years old next week. She has almost stopped growing and is in a size 18-24 month clothes. I wasn't to worried about her being small but now her hair is thinning out and her skin looks very pale. She recently has become sick, throwing up, fever, dehydration... And with her being so small I was wandering if I should go ahead and take her into the doctor.