I mailed in my tax return on March 4th and I have not been able to track it online. So this has also kept me from getting the stimulus check. What do I do?

Did you file 2018?  If the IRS hasn't processed 2019 they will send the Stimulus Check using 2018.

Just keep waiting.  They are not processing mailed returns right now.

See this IRS page for the latest information

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue

It says.......

Paper Tax Returns: All taxpayers should file electronically through their tax preparer, tax software provider or IRS Free File if possible. The IRS is not currently able to process individual paper tax returns. If you already have filed via paper but it has not yet been processed, do not file a second tax return or write to the IRS to inquire about the status of your return or your economic impact payment. Paper returns will be processed   once processing centers are able to reopen. This year, more than 90% of taxpayers have filed electronically.