IRS has no record of my tax return

I filed my 2018 tax return by mail in April of 2020, rushing to get it done in order to receive the Covid Economic Stimulus check. Here it is 6 months later and they still show no record of it. I can live with out the stimulus check, but am REALLY needing an SBA loan for my business that suffered substantial damages from Hurricane Sally. I sent my return certified with a return receipt, which I DO have. It is stamped, however it is difficult to read the month. I don’t know what to do. I’ve talked with the IRS who say that they are extremely behind due to Covid and to just give it time and please do not refile at this time, but the SBA has WITHDRAWN my loan application because of this. We are suffering. Any ideas what I can do?  This isn’t fair.