Hi there and
to the forums!
As mentioned above, your budgies should not be bred. Just because they have been mating doesn't mean that she will lay eggs. In fact, it's a good thing she hasn't yet because now all you have to do is rearrange their cage, remove the nest box, etc. and she'll hopefully be thrown out of the breeding mood.
Just because your budgie is physically capable of breeding doesn't mean it's right or healthy for her to do so. Humans are sexually mature around age 13 but that doesn't mean that it is healthy or right for them to reproduce at that time.
It is not necessary for you to breed your budgies in order for you to enjoy them as pets! Additionally, simply because "all the budgies survived" in the last two (!!!) clutches doesn't mean it's okay or healthy. As a pet owner, you should be concerned with helping your birds thrive and be healthy and happy, not just survive.
We're here to promote the best care and keeping of budgies and have the best interests of your budgies at heart! Maybe in a few years after you've done more research and owned your budgies for a while you can venture into breeding again, with an avian vet on hand.
Be sure to read through the links provided above as they include the "best practices" for caring for budgies! If you have any questions after reading through everything, please be sure to ask as we'd love to help!