I have been very lucky to be honest as I only went to the GP on Wednesday and was in Breast Clinic by Friday and only have to wait a week for my results so I know how lucky I am. Doesn't make the wait any easier though, especially when the consultant said the words 'it doesn't look great' just from looking at my mammogram before they even have biopsy results!!
It must be a worrying time for you both.
I think the reason for doing the biopsies is when they cannot be certain there is nothing from only the mammogram and ultrasound. It does not necessarily mean there is cancer just that they need more detailed information before they can say one way or the other.
It is good that they are being thorough but of course very hard on you to have more waiting to go through.
Different hospitals organise the appointments in different ways. At mine you were always told to go back to reception on the way out to make the next appointment at whatever interval you were told.