Alright. I have my own farm, so I can tell you from experience that you do eventually get used to the every day work. Hang in there, it's a transition all to itself. Make sure you stay hydrated. Being dehydrated can make you tired. Carry a bottle of water at all times. Maybe consider a camelbak for convenience. This is really important. You'll drink more than you ever thought with the kind of work you're doing.
I would follow the advice given and stick with a light breakfast for now and see if it helps. Maybe a potato and some cheese? That used to be my stand by last summer when I was trying to get out the door quickly. Also, carry something with you. I have become incredibly fond of shredded/chipped coconut. I can get it "natural" and un sweetened at my grocery store. Quick snack, fits right in my pocket and keeps my stomach from bothering me. You're only working out there for 5 hours, so, if that means coming back and making a huge meal to replenish, go for it.
This is my experience. I would advise making changes and see if it works. This is how I made it through my first year as a newbie solo farmer. You can do this.
The process is simple: Free your mind, and your ass will follow.