David,
My brother
David went from: environmental sciences to geography to sociology to environmental sciences to (finally) health. I don't think he declared all of those, but he certainly took courses in all of those realms.
Needless to say, after 7.5 years of college, he had WAY more than the required 120-some credits to graduate.
So, it's common, and you shouldn't worry. Find what you like, put your heart into it, and you'll enjoy doing it. The first semester/year is all about learning about yourself.
