Things not being considered: 1. Your religion might be yielding a few coins, up to 10 with drift, something along the way with cathedrals. Your pantheon could be giving some gold too. 2. Your luxuries are most likely giving some gold. Directly and by trade. 3. Have you counted gold from city connections? 4. If you build caravansary, your merchants give a few more coins. 5. You can work the second merchant (bank?) if you are in need of. 6. During golden ages, gold from terrain gains 1 each.