Its been over 21 days and I still have no federal refund. The IRS tool says my info doesn't match.

This is normal. It can take anywhere from a few days to 3 weeks to update. The IRS began processing returns on 2/12, you may not find a record of it or the website may say that you have put in incorrect information when tracking your federal refund. As your return moves through the system, the status of it will be updated. Continue checking the Where’s My Federal Refund tool for updates. Updates are made daily, usually overnight.

What does pending mean?

Please use this link to track your refund from the IRS

Tax Season Refund Frequently Asked Questions

It has been nearly 4 weeks. 

I don't understand why others who filed after me are seeing information on Where's my refund, and after almost 4 weeks there is still nothing on mine.