You should have done more research before attempting breeding! It's very alarming that you are referring to them as being 'pregnant'. Birds can't be pregnant, they can lay eggs, and that's it.
The breeding is not called intercourse, but mating. Lovebirds are prolific breeders, and tend to have a lot of babies in a short amount of time.
Have your birds been checked by a vet to ensure they are at the very least, healthy?
How old are they? Small birds under 1 shouldn't breed as they are not mature enough to support reproduction yet.
Why did you get them a nestbox without making sure they are both female and male, and have done proper thorough research? Your statements show me that you know very little, if any, especially with the 'pregnant' thing. Can I ask how old you are? Are you sure you want to be taking on breeding birds?
Aggression can happen and it can often lead to dead birds. This is why you screen lovebird couples before placing a nest box in the cage with them, to see how they live together first before introducing any hormonal triggers for reproduction. If they are aggressive towards each other like with the male not letting her into the nestbox, I'm sorry to say but it may not work out very well for this couple, and you could run into terrible heartbreak by witnessing attacking until eventual death by one bird or to the babies.
I'm a cockatile breeder and I don't ever put a nestbox in unless I have all my supplies ready and full intentions to remove babies from the nest after 2 weeks to handfeed with intentions of raising healthy, happy, tame babies. So let me ask you this...what are you intentions with this clutch? Will they be your pets? Will be be selling them? Will you be committed to separating femaels and males to ensure siblings can't mate with each other (it happens all the time!) What will you do if the parents abandon or neglect the babies? Are you ready to step in to handle ALL care around the clock? Hope you don't work or go to school out of the house because they'll need your 24/7 attention.
Honestly I would take the nestbox out so the pair can get to know each other better.
Always remember....
BIRDS DON'T HAVE TO REPRODUCE TO LIVE A HAPPY, FULFILLED LIFE!!!