I think it's reasonably common that when you develop some calm an mindfulness you realise that there is nothing going on between the outbreaths and inbreaths. That's a good sign --- you learned something! I'm not sure why would you want it to be different. It is what it is. So perhaps just paying attention to there not being a breath just yet will "solve" the problem.
However, if you are still losing focus then a common approach is to "fill in" the space by paying attention to something else, e.g. the touch of the cushion, or the feeling of the body supporting itself.
Exactly what is best for you will depend on how you are trying to develop the meditation, and you'd have to explain what your approach is. Are you following a particular teacher/book/website/interpretation of a sutta?