Don't be surprised if your sex drives take a bit of a dip during this two-year period. You're both feeling more tired out than usual, even if your workloads stay the same; the usual business of daily life is draining now, and you may not have the enthusiasm required to set aside time and energy for lovemaking. That's not the only effect of this transit, either.
This could be a period of general discouragement. Your relationship is hit with the blahs; all of a sudden, you're both more aware of what's difficult than what's enlightening and precious between you. If you're used to having a fast-paced, action-paced connection, this could be a bit of a frustrating period for you. Instead of spontaneity and excitement, you'll get rented movies and plenty of naps (ho-hum). Try not to judge the merit of your entire relationship on this one period. It's a long one, but it's not the only one influencing your relationship. There will still be high points and phases of passion between you; they just might be shorter than at other times. The main thing now is to try not to expect more of each other than is realistic. You can avoid disappointment if you just lower your expectations.