W-2

Last year I filed as Head of house with 1 dependent (child under age of 6) my income was only $2,340. My refund was $5,560. This year I filed Head of house, 1 dependent same as I die last year but my income was  more this year $3,704. And my federal withholdings says 0? And my estimated refund is only 1,432? Why is my return so low compared to last year also why does my withholding say 0? I did not change my withholdings. I typed 0. What has happened?