USPS May have lost my tax return. Cannot check status?

Unlike other 200 IQ folks, I just mailed my tax return in an envelope with a stamp. So I have no registered mail or tracking. I mailed it on March 22, it’s May 10, 7 weeks later, and still no sign. I’ve tried both the IRS automated hotline as well as the online tool and input my information but it says no information is available in both cases.

1. Is there any way to verify the IRS has received the return apart from the website and hotline? Or does this mean they have indeed not received my return?
2. Several points on the IRS website urge me not to resend my forms. (This seems very puzzling to me)
3. If I do not resend my forms before the May 17 deadline, will I be penalized anyway?

Should I resend forms (this time with registered mail) or just hope for the best?