What is going on with shipping?! Help!

I am an FBM seller and have like 20 orders that came in Saturday afternoon after I last shipped, and these orders they need ship today. The regular USPS ground or advantage shipping option I normally use is unavailable. Some need to be delivered by Wednesday, and the shipping cost would be about the same as the order price the customer paid. Some are even showing shipping options that would be twice the order cost. They also want me to put the orders in envelopes instead of the boxes I always use and that are set on my profile. What’s going on here? Why are they able to select these shipping options without paying for them? Why are my regular shipping options not available? What should I do with these orders?! They would cost me money the way things are. I’m in a panic!