Can anyone who knows the language well tell me if I should use since or from in the following sentence?
Here is the example:
I had a chronic liver disease from/since my childhood days. Now I am fine after the operation.
As this NGram charting relative prevalence of blind from/since birth shows, from has always been more common than since...
But it's clear that both are in use, and since is steadily gaining traction. Personally, I would prefer to use the newer form, but this has nothing to do with possible differences in nuance (I don't think there are any), and it in no way implies there's anything wrong with using from.
It may be worth pointing out that (for no particular reason that I can articulate), I'd be far more likely to say ...since I was a child/kid. In which context I'll also note that to remain syntactically valid you'd have to replace since with from when there.
Also, people would often want to emphasise how long something has been the case, which is easily done with ever since. You can't use ever with from like that - the best I can come up with is right from when I was..., but that's vanishingly rare compared to ever since I was.