Zerg doesn't need any proxy stuff. And in general cheeses like proxy rax/gateways/cannon rush, should not beat you. You need to scout properly, and use a zergling so that you know when an army is moving out towards your base. With good spine crawler placement and enough roaches, zerglings/banelings you should be able to hold off 4gate/3rax pushes etc.
I don't understand what you mean by protoss and terran 'don't drop on army count'. If they make banshees they will have less marines/marauders, if a protoss builds proxy gateways and makes loads of zealots, then he cant have a good economy (and also his base will be more open to ling run-bys)
What you need to do:
1- scout early with a drone, if you see less buildings in their base than you would expect, then they must have some proxy buildings
2- use zerglings on the xelnaga watchtowers, and put one outside their base. This way, you can see when their army moves and, and if they take an expansion etc.
3- if you see an army moving out early on, or don't see many buildings in their base (you suspect a proxy) Throw down 2 spine crawlers on your expansion (or base if you haven't expanded, and stop making drones. Save your larvae for roaches or zerglings/banelings. You may have to pull your queen to your ramp to stop them getting in your main.
The thing you have to think about though, is that if they do an early push/cheese and you dont completely die to it, for example, you lose a lot of drones and roaches and maybe your expansion. You are still usually ahead.