Do you know what your Sodium levels are like? I'm pretty sure if your Sodium is too high this can lead to acid build up then if it gets bad enough bone break down leading to broken bones. But I think the level would have to be pretty high for this.
My Sodium is on the high side but it's not over the limit.

I know there is a small chance this might be that cause but you might want to consider costochondritis as a possible cause of chest pain. It's basically an inflammation of the place where your ribs attach to your sternum. This is a very common cause of chest pain if the heart is healthy and cardiologists find nothing wrong with it. It basically starts in the inner chest but can spread to the entire chest area and can be pretty debilitating. I had it due to the lack of awareness of my shoulder mobility when working out and anti-inflammatory medication combined with better awareness solved my problem. BUT sometimes antiepileptic medication can also cause this, especially sodium valproate. It demineralizes the bones and makes them weaker making it more likely to get injured even on simple tasks. My suggestion is that you should see a physiotherapist to have this checked out especially if the cardiologist said everything is fine. There are also home made ways to check on this but I wouldn't rely on them. Your husband could try to do some push ups and if the pain gets worse then it's costochondritis, but even if it's pain free it still could be the cause so you should still see a physiotherapist. In a physiotherapy clinic they make more advanced and reliable tests that can conclude if this is the issue and can help you with treatments. I hope this helps.

I get this, but I think it's related to the medication, not the Epilepsy.