I had my son in 2001 and I want to say that I "dropped" early with him. Of course that being my first pregnancy and nothing else to compare it to, I didn't know any different. But the ladies in my office would measure my belly from under my chest and could tell he dropped. I remember that was about a month or so before I had him. I didn't care, it was nice to have the extra space for my lungs.
If you are concerned then call your OB and ask if that would be normal.