My lovebird laid one egg today?

Ok I got super happy because I thought I was going to have another lovebird but I never ever saw my two lovebirds mating because they get bipolar one minute they're grooming eachother and the next they're fighting and we have to separate them they're probrably girls but I'm not sure I know the one that laid the egg is a girl but the other its always fifty fifty the say its a she or he so idk but I went to a petshop and they told me to throw the egg cus its most probrably infertile and shell get more aggresive so I threw it away because they're always fighting now and separated we have a divider in the cage. So yea she seemed weak after laying her egg I jst want to know what the average of them putting empty eggs and is it normal to be kind of weak after laying her egg