I filed my tax return by paper about 8 weeks ago, and I still have not obtained my refund. No information on the Where's My Refund website. Should I be worried?

I sent in my tax refund using certified mail which says that it has been delivered since around March 26. However, I am getting nothing from IRS when I look it up on the IRS website - not even "processing", just "no information". I don't mind waiting, but I'm worried that my tax refund got lost in the process. Should I send in a new copy of the tax refund to the IRS? Or should I just keep waiting.