Deductions & credits

My child is almost 5 and disabled and I (her mother) am claiming her and filing separately from my now ex-husband. She has lived with me her whole life and I'm still not receiving her child tax credit. I filed as head of income, claimed her as my dependent which she qualified for but when I did it actually made my tax return go down instead of up. Why did my tax return go down instead of up and why am I not receiving her tax credit?