Trouble stopping protoss from expanding

Hey so i am a terran player 1v1 and anytime i face a protoss the map is so huge that i find it very hard to scout the entire map out every few minutes and the big issue is that protoss then starts expanding and has like 3 bases while i struggle to expand anywhere that is not close to my base. The biggest issue is the observers they are invisible air units that own at scouting. So how does a terran stop a protoss user from getting so many bases up? I have also tried attacking the protoss players weaker expanded base but it seems that he also has a huge army there and then i am vulnerable at my main base I usually use my sweeper scan to check every few minutes on what he is building so i can counter his units.

 

One thing i would suggest is to keep up on your scouting, that will let you know when and were your opponent expands. Scouting plays a major role in this game, so basically just get better and keeping up with your scout rather it be your scv or comm

 

You might want to think about putting a SCV on a watch tower to observe the map and look for probes going to get expansions. Also maintaining map control is the best way to keep a player in their first two bases. also your terran, you should have no problem lifting to an easily defended base.

 

putting up towers or even just turrets, since they are cheaper, at expansions, if you can afford it, helps. that also helps catch the random observer too....which may be what he is using to keep track of your movements.