After you file

There's no reason to necessarily be concerned, so please don't worry.  The bars on the IRS.gov's "Where's My Refund" webpage (which it is believed you are asking about) change all of the time.  Not all tax returns are identical, 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, including those of the PATH act.

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 such a 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 your tax return 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, 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.