If you have not received your refund from the IRS and you filed over 3 weeks ago, the IRS may be still processing your return.
If there is an issue you should receive a letter from the IRS telling you what the issue is. Without this information there is not much you can do currently.
Once the IRS opens its phone lines again, if you still have not received your refund, you can call the IRS at 1.800.829.1040.
@Dria