Can a night guard change my bite?

Hello. I have 12 veneers/crowns placed on my top teeth, and my dentist recommended a night guard to protect the restorations from damage. I have been wearing it religiously the last five months, but have noticed a change in my bite. When I had the treatment performed in June, there was less space between my top and bottom front teeth. This space seems to have increased. I wear the mouthguard on my bottom teeth. Is it possible that the mouth guard is pushing my lower jaw or teeth back?