Nothing changed? Your standard deduction nearly doubled, so using itemized deductions became much, much harder to do. Personal exemptions were eliminated. Employers were given a new table for withholding federal tax, so most likely you had less withheld from your paycheck--although your weekly take home may have been higher. There has been a cap on state and local taxes paid of $10,000, so again, your itemized deductions may be suffering. Job-related expenses for W-2 employees have been eliminated. Medical expenses are subject to a 7.5% of AGI floor. Moving expenses have been eliminated for all but active duty members of the military. And those are some of the highlights for the new tax laws.
Compare your 2017 W-2 to your 2018 W-2 to see what might have been different in box 2 for federal withholding. Compare 2017's tax return to 2018's return line by line.
And of course, always check your own data entries, looking for errors such as misplaced decimals or extra zeros.