unless you have very high income say over $200,000 this should not be. however, there are certain things that can affect your taxes. alternative minimum tax, net investment tax, loss of credits like earned income and education credits. we can't see your return so we can not give you a specific answer.
you may want to check your taxes using either the IRS 2019 tax tables (up to 99.000 of taxable income) or tax rate schedules. in the tax tables (page 73) the tax for single and married filing separate are exactly the same
$17,929. However, this does not take into a/c credits, alternative minimum tax, tax on net investment income.
look at your returns line 12a through 16
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
