Could your decrease in drive be related to any stress in your life? Maybe school, work, relocating, physical health, mental health, etc.? Perhaps you could work on other issues and that may help reinstate it. If not, maybe your emotional relationship needs some work. Have you tried talking about this with your boyfriend?

Recommendation-wise, I would say that trying new things and being as open as possible with your partner could help quite a bit. If you feel like it's become a serious problem, perhaps talk to a counselor or doctor about it! They might be able to give you some good, extremely informed advice.

I have no idea whether or not there is something wrong with you. In terms of sexual highs and drive, however, you're right on the typical brain course. After about 6-24 months in a sexual relationship, the brain's "hit" diminishes. Couples who choose to stay committed to each other typically move from a position of staying together because of the hormonal tsunami to one of deeper love and long-term committment. Although couples can be creative in terms of keeping sexual activity fun, the next stage really is choosing to stay together because of the qualities they see in each other. Some individuals never get past the intial euphoric stage. As soon as the hormonal tsunami dips, they look around for someone new and more exciting so they can get back to that initial high. Some spend their lives moving from one relationship to another.