Still conflicted with this job

I've been at my job over a year and right from the beginning it just hasn't been right. I was poorly trained and have struggled constantly to get into what this job is all about. I was hired for my knowledge of agricultural animals but what I do deals most in ag equipment. My background is only about 5% of what I do. I have people asking me questions about the equipment, or asking me technical/engineering things, and I do not have a clue how to answer. These are all things you do not just learn over night either. All of my colleagues have 20+ years of technical experience while I have none. This job is like a bad relationship... When its bad, it's really bad but every once in a while its great. I have some possible projects on the horizon, but this still doesn't feel like what I want to do. It's been taking a toll on me emotionally too. My DH and I got into an argument while I was on a business trip out of town because I was so stressed from work. I also feel like this job is not conducive to our plans for a family. I'm out of town a lot and when we start equipment up, I work 12-16 hour days, for a week, of hard physical labor. The biggest issue is that I don't want to feel like a quitter, or like I didn't give it my all, but it eats away at me. Some days I sit here and think "man, I hate this." I also make more money than I ever have and am not sure I would ever find anything that pays as much in this area. What do I do? Keep trying to become good at this or look elsewhere? Has anyone ever had this happen?