Game 4:
You go out to clear the watch tower, clear it and come back, but never actually leave units there to hold it ; ; pls scouting.
Position your turrets better. You waste a lot of minerals on unnecessary turrets...you could be building an additional CC with that money.
Your play was SO MUCH BETTER this game. You were dropping and pressuring. Ladder drop during the attack. Tanks were better spread and sieged in time.
Engage @ 20: 2 tanks balls deep in the front. Too far out

probably lost you that engage by themselves.
@21, marines die, run the tanks back and wait for more marines. If he had been smart he would've killed all your tanks instead of half.
Good hold against the broods. You lost a lot of vikings due to poor control/not moving up marines to support but you ended up surviving.
Watch games 2 and 4 again and compare your vision around 11 minutes in both games to the Zerg's vision. Every game your vision extends to the edge of your base...where as the Zerg has units spread all around the map, lings patrolling, blocking expos, holding watch towers. You need to be the one with that sort of vision or you won't be able to progress.