Can anyone please tell me if I should you since or from in the following sentence?
I think you mean "use," Subhajit.
1- I had a chronic liver disease from/since
my childhood days. Now I am fine after the operation.
2- I had a liver operation in my liver last year because I had pain in my upper abdomen. I had had a liver disease since/from my childhood.
Example (1) would be better with the present perfect rather than the simple past. Then you can use "since my childhood days" or "from my childhood days on" ("on" is an important addition: "from then on"):
(1a) I have had a chronic liver disease since my childhood days, but now I am fine.
(1b) I have had a chronic liver disease from my childhood days on, but now I am fine.
Example (2) is fine with "since." If you use "from," add "on" after "childhood."