Terran Fortifications

I have no idea how to handle Terrans in the mid to late game. My statistcs on iccup right now (currently I am 3-3 vs. Terrans) are wildly misleading. First of all: I rarely encounter Terrans and when I do they are often pretty bad. If they just manage to keep up into the mid game I know I am dead.

So what makes them so problematic?

1. On equal supply, they win. When we both have maxed out our armies, then the Terran will win.
2. If he can manage to secure an expansion somewhere with a ramp, it is probably his until it is mined dry. A couple of tanks, turrets all around and mines and my only option is carriers. Something he can easily counter with goliaths.
3. Scouting. If I could just figure out if he fast expanded or did an early two factory attack, it would help a lot. I need to know this before I get observers and he is most likely walled in. I know there are signs like an early siege mode probably means fast expand, but it does not seem reveal itself early enough.
4. Turrets. Most Terrans at my level build at least 4 to 6 turrets around their main around that finishes about the same time as my drop would arrive. That makes drops largely ineffective, but somehow the cost of 6 f*ing turrets should give me a huge advantage when I do something other than a drop. Somehow it does not give any advantage to me.

I’m at 50% wins against Terrans, but I feel much more comfortable playing against another Protoss and I am only winning about 35% of those games.