Sounds like you expanded a bit too fast. I seem to do that all the time. But, that doesn't help you now. If you have the $$ buy lots of mercs. If you can't do that, you may need to retreat a little to consolidate your forces.

Are you actually at war with the pope? If not, leave a small army there as a deterrent and go have some Froglegs. If you're at war, then see above paragraph. And next time, pull out of the pope-held provinces and let them rebel before the pope returns; IIRC, he won't be at war with you then, when he returns.

Third option: borrow some of that $50K you gave your allies.