Only the IRS (or state) can answer that question. Once your tax return is accepted TurboTax is out of the picture and receives no further feedback from the taxing authorities. The taxing authorities will not give any information to anyone other than the taxpayer.
Did you efile, or did you print, sign, and mail the return?
Here are some things to check. Sign back into your Online account (assuming you used Online TurboTax). What is showing for the "status" of the 2018 return? Does it say accepted, rejected, printed, started, ready to mail, or what?
If that showed it was accepted (or if you mailed the return), what do you see at the IRS website below for the status of your Federal refund?
NOTE: When using that tool, use only the Federal refund amount, and not any total refund amount that includes a state refund. The amount to use is on your Federal Form 1040, Line 20a.
If the IRS tool says it is still "being processed", here's how to speak to a live agent at the IRS to see if they can tell you anything about the delay.
IRS: 800-829-1040 (7AM-7 PM local time) Monday-Friday
When calling the IRS do not choose the first choice re: "Refund", or it will send you to an automated phone line.
I usually use a speakerphone so I can work on something else while waiting.