My 9 month old daughter isnt crawling at all, isnt walking, wont pull herself up on anything, and every time i put her on her tummy she rolls right over to her back and than cant move. She still is completly immobile. Should I be concerned?? She isnt overweight, she weighs 21 lbs, and she is 26 inches, all the other children her age are about walking, and she cant even scoot.