Hard to say from the detail you've provided.

I find sometimes when I enter a big expansion phase I spend a lot building new armies and the upkeep gets out of hand. Particularly if you've got big garrisons sitting in cities that aren't producing much yet. If you're destroying and rebuilding buildings that soaks up money fast as well.

If the problem is that your army upkeep has grown faster than your income, the best thing to do is stop ordering new troops, draw down your garrisons, make new attacking armies, and take new territory. Preferably rich territory.

Rhodes is typically a big moneymaker. When in doubt, take Rhodes.