Since you stated that it might be too early for the birds to have an egg so soon after mating, unless they have mated previously without you knowing it, I want to mention that adult female budgies can lay eggs without ever having mated. The difference is that the egg won't be fertile. I had a cockatiel once who did the same thing, and she wouldn't have anything to do with the male who lived with her. If we took her infertile eggs away from her she would simply lay another clutch until she got 'motherhood' out of her system. If you can get your hand in there without getting pecked, you could gently grab that egg and 'candle' it, by holding it up to a bright light. If there are stripes of veins on the inside, the egg is fertile. If it's just a blob, or you see nothing at all, the egg is infertile. Also, you mentioned that the male is eager to mate every time the female emerges from the nest... perhaps he should be removed from their living quarters and placed 'next door' in another cage, during the duration of this process. Also, eggs require a certain amount of moisture in order to hatch live chicks, so if the female isn't getting enough water to bathe in, her skin may be too dry and that could have a detrimental effect on the eggs. Even a gentle misting every so often from a water bottle would probably help as long as the nest isn't completely saturated. And of course, give her time, as all good things come to those who wait. Make sure she's well fed, well watered and can bathe at will and also, make sure that she is warm enough. Temperature is extremely important when hatching eggs, and budgies are exotics so they need warmth. If she's getting a draft from somewhere, move the cage or nesting box to another location. Practice makes perfect, both for the pet and for the pet owner as well, so remove all 'obstacles' and keep trying. Good luck.
