Hiya Shez
The reason I ask if your period was late is because there is every possibility that the heavy bleeding could be an early miscarriage if very different to your normal AF. Many women will have an early miscarriage and never know as they assume thet have just had a late AF.
Whilst homonal changes are usually the cause of heavy bleeding, as you have been taking Agnus Castus for a few months, it it worth considering the fact that you may have achieved pregnancy, but sadly it was not to be.
Although the onset of bleeding means you may never know whether a pregnancy took place, it's worth bearing in mind as it means you can and will get pregnant in the future.
Hope your periods settle down soon and you achieve your BFP very soon!
Best of luck!