I just started ortho tri-cyclen lo about two weeks ago and my boobs have "exploded" too, as you put it. They're kind of small to start, so its probably not a big difference, but they seem huge. I had the same thing happening before my period before I started the pill, too, so I wasn't terribly surprised when this happened. Its just a pain that it appears to be a perminant thing now. So I guess if its an abonormal thing, you're not the only one.
On the plus side, I think the ortho tri-cyclen lo is supposed to be a lot lower hormone dose, so maybe you won't keep having the problem when you switch.