The IRS started processing returns later than in prior years and as such has a backlog to work through.
Refunds are generally processed within 21 days after acceptance.
The general timeline of e-filed returns is: Transmission > Acceptance > Processing > Approval > Refund.
After acceptance, but before processing, if you contact the government or try look up your refund status while your return is still pending, don't be surprised if they tell you "no record found." This is normal; until the government starts reviewing and processing your return, they won't have any record of it.