I have a lavender Orpington that she is just old enough to start laying eggs. She’s at her fifth egg that she’s laid so far I see that the rooster is mounting her, but I don’t know if the eggs are fertilized because she will lay the egg but will not sit on them. I have three in the incubator. That shows no signs of being fertilized. They’ve been in there about three days now I’ll keep them in there for a few more days, but I just put another one in there. How do I know for sure if they’re fertilized?
She will not set on the eggs until/unless she goes broody, and that won't be until she is further into her laying cycle. Pullet eggs can result in stunted chicks. I would wait until her eggs are larger to incubate them. Collect the number you want to incubate and start them all at the same time. Staggered hatches, even in an incubator, result in problems.