Suggest Treatment For Excessive Crying And Involuntary Shaking In A Baby

I have a baby 18 month s she weight 16 lbs. she wakes up shaking some times she can move her head to the side for hours she can not walk yet she can sit for awhile but will fall over. she crys a lot like she is in pain . her thumbs lye flat in her palm of her hand all the time her little finger curves out. what is wrong with her?