The IRS started processing returns with the EITC and ACTC credits the last week of February. It could be that your return required additional review which causes an additional delay. Please see Why do some refunds take longer than others? for more information.
If it has been over 21 days since your tax return has been accepted, please see What if my IRS refund is taking longer than 21 days? for information on contacting the IRS.