I had pneumonia once as a kid, and it left me pretty susceptible to it.

Since then, I've had full-blown pneumonia once and walking pneumonia several times as an adult. Every time it's taken me at least a week to return to feeling mostly human, and several weeks to feel confident doing anything resembling exercise.

Don't push yourself too hard, too soon. That's a quick path to making yourself more sick and stretching your recovery time out even further. It sucks, but patience with your body is your best friend here. It just takes time to heal.