I was a total fanatic when I was an undergraduate student. If a professor mentioned a book, even in the context of “book X by critic YZ is worthless”, I immediately dashed off to check book X out of the library and read it. I counted down the days of each break because I couldn’t wait to get back to class. I once left a New Year’s celebration because I had a textbook on medieval literature waiting for me. Nobody had assigned it. I was reading it for fun. I read Juan Rulfo’s novel Pedro Páramo three times in a row without even looking at the translation until I somewhat understood it (this was less than 2 months after I began to learn Spanish).
And I loved every second of all of the above.
If you don’t feel this way about your field, please reconsider doing a PhD in it.