Who knows??? That can happen. Did you claim the EIC or Additional Child Credit? The IRS is holding those.
Was your federal accepted? First check the status of your return here
https://shop.turbotax.intuit.com/efile/efile_status_lookup.jsp
You can check your refund status at Where's My Refund. This is for your Federal Return.
https://sa1.www4.irs.gov/irfof/lang/en/irfofgetstatus.jsp
And see, IRS warns of refund delays
https://www.irs.gov/individuals/refund-timing