With most lovebird species, you can’t tell the sex of the bird without a blood test. So even though they seem to be mating, the lack of eggs could mean that both birds are male. There are a lot of things to do to get a pair ready for breeding. They need to be eating a nutritionally balanced diet like pellets or our foraging foods. A loose seed mix will not provide the nutrition they need. You should also offer dark leafy greens and chopped veggies. They need an egg food when they are set up for breeding. You can offer a commercial egg food, or cook an egg with the shell washed, crushed and cooked with the egg. The female needs this because she uses a lot of protein and calcium to form an egg and the parents will also feed this to the chicks along with the other foods. The nest box needs to be the right kind of box, and it should be attached to the outside of the cage as high as possible. The cage needs to be in a quiet, private area. You should only be around them to feed them and do a quick check. The parents have to feel safe or they will not lay eggs. If you have done all of this, and there are still no eggs, then you may have two males or the female may be infertile. It takes a lot of patience to breed birds and you have a lot of waiting. Some pairs never make good breeders. All you can do is provide what they need, give them privacy, and hope they nest and lay eggs.
Thank you for asking Lafeber,