The IRS is currently not processing any mailed returns and hasn't been for some time. There are stacks of unopened returns sitting in IRS offices. They have not indicated when they will resume processing mailed returns. No one will know whether your return was received or not until the IRS opens up all the unopened returns. Unfortunately there is nothing you can do about it at this point.
When the IRS does start processing your return, you can track it on the IRS tracking web site:
https://www.irs.gov/refunds
See these Q&As for how it works once the IRS starts processing a return: https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions
