relentlessness

Yes, anything worth doing is sometimes hard, and can at times become something of a grind. Particularly if it's your first HIM, it's a big step up in volume for most people, and the hours get pretty long at some point. Fitness also doesn't usually increase in a linear way, which can be frustrating--one tends to plateau for a while before making progress. And with training for longer events in particular, cumulative fatigue can cause you to seem to temporarily lose fitness--going slower at the same effort, higher than expected heart rates for pace/power, etc. Some of it is just part of the process.

But you might also take a look at recovery. Are you taking regularly scheduled easy/active recovery/rest days? Recovery weeks every 3-4 weeks where you do substantially less volume? Also look at sleep--are you getting enough? With iron-distance training, you'll most likely be needing an additional hour or so on top of the 7-8 hours that most adults need (but often don't get). Finally, what does your diet look like? Are you eating enough extra calories to support the additional training load, and getting a good balance of protein, carbs, and healthy fats? Many athletes, especially women, tend to eat a diet that's too low in all of those, as well as iron. HIM (or, worse yet, IM) training really isn't the best time to follow a restrictive diet or try to lose weight.

Finally, if it's mostly mental, can you change things up a little? Try a new running route or do some trail running, or find some people to train with, or do some biking as part of a spin class, or something? I train probably 95% solo most of the year, and often I find that what's really wearing me down isn't so much physical as mental--just getting bored sometimes with my own company!

X2 for the above reply.

I'm training for my second HIM this year. Long bikes have always been boring for me, especially when on the trainer. I zwift which has helped a bunch.
I too am working on heart rate zones as well and end up having to walk a lot more than I need to. In the end pace ends up being slower than I want or am capable of but I also know to trust the process.
Once we learn to let go of pacing it does become more fun again. Find somebody to run with. That helped me a lot. My training partner and I run together once a week for at least an hour. She is one of the few people who I can talk to on longer runs. The fact that we don't talk on a daily basis helps, because there is always something to talk about.
Rest days a critical. Be sure and take a day off if needed. Your body knows what it wants and needs. You don't want to get an overuse injury that could keep you down for a while.

Agree with the Saigon Queen.

FWIW: I love training (& the bragging rights). That said, perhaps you are doing too much/too soon &/or is this YOUR "thing"?

OMG! I think my fellow fast female triathlete (Sophie, 25, about my speed overall, but way faster on the bike and getting faster all the time while I am getting older and slower) might take exception to that. Or maybe she can be the princess?! We do have a king here (in 50-54, he did Kona last year), as well as a 30-something prince. Guess we are set as far as royalty goes.

I definitely agree with the posts above in regard to recovery and listening to your body. It's amazing what a few nights of good sleep can even do.

However, for me when I start to feel "down" or in need of motivation it only takes reading a few inspirational quotes or seeing something on TV that puts me in the frame of mind that everything is relative. I mean, can I really be complaining about running 3 miles when there is so much in the world that I should be grateful for? There's going to be one day that I won't be able to do this stuff and I suppose I use that line of thinking just to push me a little bit more.