The relationship may suddenly seem very restrictive, not at all the fun-loving, freethinking bond you wish it could be. Even if a week ago you were both reveling in the commitment you've made to each other, when this period sets in you'll both start to feel like a horse in captivity, chomping at the bit, wanting nothing more than to run wild and be free! So why can't you do that together?
The simple answer is that you can -- you just don't realize it right now. The only thing that has changed, after all, is your perception of your bond and what it brings to your lives (or takes away from them). If you're looking at the relationship as something that hems you in with obligation and duty, then of course you're both feeling strained! It's possible that this influence will affect you as a unit, of course, such as if there's an outside force -- parental expectation, maybe, or career issues -- that place limits on you that you don't want to submit to -- such as the expectation of marriage when you're both fine with your relationship the way it is. Just try not to throw out the baby with the bath water when you make those changes you're chafing to make.