Protoss armies are stronger than yours. They always will be. If they aren't, they're doing it wrong.
Protoss hard counters do better than yours. If they get 4 or 5 collosi, they can one shot your hydras with focus fire. You have to overproduce collosi to such an amount that their stalker ball will beat your hydra/roach and you have to replenish.
Zerg, unlike protoss and terran, don't have the ability to tech up, get a strong economy, and get a good army all at the same time. We can get a good economy, a good army, or tech quicky. We only get one, they get all three. Past early game when you get towards the mid game though, you're suddenly able to do any of those three (still one at a time, pretty much) much better than your opponent. You can fully saturate an expansion almost instantly, you can build one building and suddenly be able to produce twelve of that unit rather than having to build multiple buildings to produce it, and you can create dozens of units at the same time.
So scout your opponent. See what he's doing. React accordingly by picking either eco, army, or tech. Try not to do more than one in a phase. Make a few lings for defense or some spines, sure. Get your lair if you can, sure. Make a few extra drones when low on gas instead of roaches, sure. But really, pick one that is best for you and use that.
Then, once you get a good handle on that, react accordingly. Strong tech should give you some sort of control, whether it be map control (muta) or confrontation control (casters or units that hard counter T1 like hydras vs. stalkers in low numbers), strong econ should give you more options down the line, and strong army should give you the ability to go on the aggression.
