Why Did I Gain Weight?

I'm in college and swim Division 1. I also run on the treadmill when I don't swim, sometimes up to 8 miles. I like getting very hard workouts in every day and I rarely ever take days off - I don't think I've taken a rest day in about a year.

Anyway, about 3 1/2 weeks ago, the team went into its "taper" for championships. Basically this means the practices over the course of this time were much shorter and much easier than our normal mid season practices (they were about an hour long on average; normally between 2500-3500 yards). Since we normally swim 6000 yards, I knew that I would have to go work out in the gym in addition to the practice to get my full workout. However, for me, it's very hard to run AFTER swim practice because the water is so cold and it makes my legs very stiff. Therefore, for this 3 1/2 week long period, I began getting up early in the morning and running 4 miles on the treadmill. I would then eat breakfast, have lunch a little later, then go to do the taper practice. Basically I was working out twice a day. The overall AMOUNT of exercise time I was doing was the same - it was just that I was breaking it up into 2 separate sessions rather than one long one (such as our typical 6000 yard practices, or practicing for taper and then immediately running afterwards). I knew that as I started this routine I weighed ~120 pounds. I did not change my diet at all during this time. I eat very clean: vegetables, lean protein, fruits, egg whites, etc.

Well the other day I weighed myself for the first time in about 3 weeks and I weighed 126 pounds. I gained 6 pounds. I started freaking out and I still am freaked out. I believe there are two POSSIBLE solutions as to why, and I am just wondering which is the more likely scenario.

1) I gained fat. Since I broke up my workouts, I was not working out for a prolonged period of time with my heart rate up. It needed to get up to where I was really working hard at the start of each workout, which hampered my ability to burn calories and fat.

2) I gained muscle. Since I was working out twice, my body was getting two very different kinds of workouts about 8 hours apart. It's very strenuous to work out twice, and my body adjusted by building muscle.

Which is the more likely scenario? Overall I don't think I look any different (no additional fat yet no additional muscle). Help!

You know that's not much at all to weigh, especially for a guy, right?

That aside, I doubt you put on fat given how active you are and how many calories you must be burning in a typical day.

Does anything wiggle? can you pinch actual fat?

I believe you said no, so..why ya worried?

You're in great shape.

Don't know how much protein you're consuming in a day, but if you feel it might be an issue, you could up it.

I've always been able to pinch a little fat which never bothered me, but I don't see any difference in muscle, I don't feel stronger, and I don't look any more cut, so that's why I think it could possibly be fat.

And in terms of my protein, if anything i'm getting more than enough. I know I really shouldn't but I try to restrict my carbs as much as possible with the exception of fruits and vegetables (ie no bread, rice, pasta, potatoes, starchy vegetables like corn, peas, and carrots). I MAINLY eat grilled chicken, fish, egg whites, whey protein shakes, natural peanut butter, lots of green vegetables like broccoli and spinach, and then moderate amounts of fruit like apples and bananas.