When someone expands early there are generally 3 options that you can go for.
Match him expansion for expansion: This will allow you to keep up economically with him and will give you a better chance at winning a macro game. This plans for the long run option of the game. If you don't go this route, as you mention they will probably win with better macro. With the proper use of mules you shouldn't fall behind to a protoss on 3 base, even with chrono boost being used. You should be able to keep up. Especially if you don't take gas and pump out nothing but marines for defense and scvs.
Apply pressure: This will require you to do something like dropping 5 or 6 more barracks and just go for a heavy heavy push that needs to do damage. Damage can be something as simple as knocking off one of the expansions or killing lots of workers or knocking out a key tech structure (Cybernetics core, robotics facility, robotics bay, star gate, etc.). This will push them back technologically and allow you to get your third base up or to keep applying pressure with your units. A +1 attack and stim timing push can do a lot of damage if executed at the right place on the map.
Tech up quickly: Going for something like cloaked banshees really quickly will punish him for expanding so quickly. Or even something as simple as 2 medivacs to go with a stim timing push will make your infantry army that much stronger. Or get seige tanks quickly and do a siege tank push on his 3rd, or even into his natural and up to his main. Quick expansions biggest weakness is low tech. So if you go for quicker technological upgrades then you have the tech advantage and can use that to win you the game.