I guess if it's unusual for you then getting it checked out can't hurt... I personally never settled into a routine with mine, ever since I first started I've been completely all over the joint (with both timing and heaviness etc) to the point where I can only know when it's due if I'm on the Pill...
So if that was happening to me I probably wouldn't think twice about it, but obviously it's not normal for you so a quick visit to your GP might help
Sorry I'm not much help, I can't even suggest any possible reasons for it to be doing this to you!!