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