Maybe there's a problem with your build order.
8-pylon
9-assim
11 or 12 gate
Once the gate is done get a cyber
Then robo, range for goons(or you can skip this for later), second gate
Then an obseratory.
Scout the enemy with obs and react accordingly.
If he's building a bunch of turrets, don't worry, be happy. :grunt
Take 1 or 2 expansions. Now that you're ahead of the terran, you should be able take it from here. Keep obs around his base and around the map AT ALL TIMES so you can keep track what he's doing and maintain map control.
In other words, if tries to expand, then shut him down. HARD
If you can't shut him down, then just expand yourself.(as long as you stay ahead)
Sooner or later, you gonna have to finish him off, in which case do what said before.
Hallucination can be good,too.