Maybe a few details?

How far are you riding a day? Terrain? Gearing? Weight?

Is it possible to completely unweight your bike... transfer it all to your riding buddy? Box up what you don't need and ship it home?

You may get better with a couple of days rest, but you still need to do some serious changes to your trip.

• Lighten the load?
• Decrease weight?
• Decrease mileage?
• Decrease speed?
• Perhaps take the train from city to city, then ride the bike around the city and to surrounding small towns.
• More rest days?
• Call it a false start, go home, and try again later?

I'll take drugs for the occasional break-through pain. Get off the bike and the back is killing you... Knock down the pain at night, and hopefully it is good the next day. But, I won't use the drugs to keep doing what I've been doing that cause the pain. Maybe use them one day?