Everything AKKeith said is spot on, probably because we are in the same unit lol...but one thing he didn't really touch on that I think is important to know is that it sucks (in case you didn't figure that out yet). The life of an infantryman is often boring and repetitive, repetitive and boring...and every now and then you get to do the stuff you actually signed up to do, the stuff you read about in books and saw on tv. There are many late nights and holidays not observed because you're out doing training that you've already done a thousand times and you're wondering why it's so important to keep doing it while everyone else is off and enjoying the weekend. In a light infantry battalion you walk everywhere. There have been many field ops, especially this past year, where you will walk with all your armor/gear and pack 6-9 miles then spend three days buddy rushing on a live fire and maneuver range (day and night), then walk your tired and dirty ass back through the hills home. This is the very essence of a grunt.
You will chafe.
You will bleed.
You will be tired, sore, wet, hungry, and miserable.
...more often than you will be stoked on what you're doing.
But this is the life you chose. Never, ever forget that. Almost just as important, never forget why, and never forget that no matter how shitty you think your situation is, your brother in an adjacent unit is suffering much more than you are. And there are more of your fellow Marines overseas putting foot to ass on our enemies who are suffering on a scale that makes them want to go back to when they were just "training". Remember it's not that bad.
PMA will get you through anything. Positive Mental Attitude. Good luck with whatever path you choose, but make sure you know why you're doing it.