When you log into the IRS.gov's "Where's My Refund webpage, do you receive any message that they haven't received your tax return at all?  Or is it simply a case of having no progress bars indicated on the screen?

If the second question is true, then there's no reason to necessarily be concerned at this time, so please don't worry.  The bars on the "Where's My Refund" webpage change all of the time; they can come and they can go.  This is absolutely normal.  Not all tax returns are identical either, and so they move through the IRS processing system at various speeds.  Other factors causing delays and increased refund processing times this year are several new laws and executive orders that the IRS has been charged with implementing.

If your tax return is chosen for further review, then the website should state that clearly, and also let you know to expect an IRS notice by mail.  (You haven't observed that happen, have you?)

Taxpayers who do have their returns held for review, and who expect to receive an IRS notice, tell us that this message appears clearly on the Where's My Refund website.  The behavior that you observe in the graphical bars is more likely an indicator that the IRS has received your tax return, and that it is moving normally through the processing system.  It could also be that the IRS is checking for additional information on something related to your tax return . . . perhaps causing a small delay.

If enough time passes after filing (21 days after e-file, or 6 weeks after paper file), and there is no new information, at that time the IRS indicates that you can call them and ask for assistance, using the phone number provided on their Where's My Refund website.

For now, the best recommended course of action is patience.  The IRS doesn't always move as fast as taxpayers would like (especially when waiting for a refund).  Also, as noted above, the 2016 tax year may be particularly slow, due to factors that are outside of our control.