Emily, I can kind of relate to what you're going through. When my DH and I got married 3-1/2 years ago (me age 42, him age 51), we had already been ttc for a long time. I was unhappy with my career at the time and it made sense for me to quit my job and move to where he lived, rather than the other way around. I got pg on our honeymoon, but lost that one. Even though it was heartbreaking, we were hopeful that we would conceive again soon and have it work out. So I stopped thinking about my career. My plan was to be a new mommy and put my professional life on hold for a year or two. Great plan, except that new mommyhood didn't pan out for me, so I had the stress and heartbreak of IF, plus I had lost any sense of identity (no more career, new community with no friends or family, workaholic DH who was never home). It was terrible. (Still is hard, but I'm on better footing now on several fronts.) I have since started a new career, self-employed, and it's going slowly but fine. It has helped my grief, confusion, and depression so much to feel good at something and respected.
So I can relate to your feeling lost because your Plan A for the next chapter of your career has fallen through. So soon after Plan A for having a 2nd child fell through for you. When one aspect of our lives causes pain, it's natural to reach out for other "railings" to steady ourselves. And if those other railings are shaky themselves, it's very disorienting. You're just not feeling much control over your life right now, so I can see that it would be comforting to have your career all figured out. But what's that expression?: "The sound of God laughing is people making plans."
It's so true. (at least in my case!
I would suggest you treat this career plan loss just like you're treating the DE issue: give it time, keep exercising, do things that make you feel happy, have faith that this is just one door closing and that there will be other doors. you'll start to feel hopeful again soon.
One idea: have you ever worked with a coach? There are many kinds (life, career, leadership, etc.) but they all do basically the same thing: help you find your own answers to your challenges or clarity for your confusion. I happen to be leadership coach, but a lot of the issues my clients have are general career or life issues. I bet there are coaches near you. (I think I remember you're in New Zealand?) If you're ever interested, I can put a feeler out for you in the alumni community where I got certified. Perhaps there's someone in your neck of the woods. Most coaching happens over the phone, anyway, so it wouldn't even have to be really close to you. It might help you to feel more proactive about your future, instead of helpless and confused (totally projecting my own former emotions on to you!!
Just a thought.
Anyway, hang in there, and take good care of yourself.