Weight

Exercise is not required for weight loss, but a calorie deficit is. A couple things that could be happening:
-If you are a woman who menstruates, water retention due to hormones could be masking your weight loss. If you see no loss in a full menstrual cycle then you can rule this one out.
-You may not be in a calorie deficit because your eating more than you think. This could be due to not logging EVERYTHING accurately. It’s really easy to nibble through a couple hundred calories, over fill a measuring cup, inadvertent use an incorrect food entry and underestimate your calorie intake. If you aren’t already, use a kitchen scale to weigh your food rather than measuring. And consider having a week where you’re only eating foods that you have a good chance of logging accurately (nobody adding oils and butters to your steamed veggies, or other things restaurants do to make the food so
yummy).
-You may not be in a calorie deficit because you’re not eating enough. When we don’t eat enough our energy level drops and that couch looks so much more inviting. And we stop fidgeting, and we park closer to the store and take fewer steps. I’m not convinced that this explains 100% of your lack of loss, but combined with the others above, it could definitely be a factor. I’ve found that keeping the deficit at no more than 500 calories a day (probably closer to 1400 calories a day for someone of your weight) is more sustainable. I’m about 4.5kg lighter than you and have 1600 base calories and generally eat around 1800 per day with eating back exercise calories. I am losing about 0.25kg/week, which I’m happy with. I’ve lost at a higher rate, but that took an unsustainable level of mental and physical energy for me.

Best wishes. Please provide more details and questions if anything resonates with you.

Reasonable advice above.

Question: When you say your weight has not moved at all, is that literal? Like no change whatsoever in the scale reading, same exact number? If so, check the scale's batteries, if it has them. Or reset the scale by stepping on it holding something heavy, then back on without the heavy thing.

If not literally no change, what have you observed? Is it ups and downs around the same reading, or just slower loss than you'd like, slower than previously? (If that, be specific.)

I'd add this:

If you were losing at a solid pace before the recent 3 weeks, didn't change anything in your routine (eating, activity including non-exercise movement), then weight loss stopped suddenly, the likely explanation is some variation on water retention shifts. Those can last a surprisingly length of time, especially in women who have monthly cycles.

I'd encourage reading this, especially the article linked in the first post:

https://community.myfitnesspal.com/en/discussion/10683010/the-weird-and-highly-annoying-world-of-scale-fluctuations/p1

One thing that can cause increased water retention is the stress of too-low calories (shooting for aggressively fast weight loss). The mechanism is believed to be cortisol increase. I agree that 1200 calories is likely lower calories than reasonable for your current weight & circumstances. (Noting that I have been that weight, on the way down to goal.) Your maintenance calorie requirement with your active job could be in the low 2000s, which makes me speculate that you're trying to lose a kilogram per week, or close. Half a kilogram might be OK, but 0.25 might be even better.

Check this: https://bodyrecomposition.com/research/dietary-restraint-cortisol-levels

I'm not saying you meet that extreme personality profile, but the article explains the basic issue with cortisol and attempts at fast weight loss.

On the other hand, if you were losing weight at first, maybe a big jolt at the very start, then your loss rate gradually slowed . . . that tips the probability toward the explanation that you've found maintenance calories, or close. That can be from undercounting, it can be from some degree of fatigue (perhaps subtle) reducing your daily life movement, or a combination of similar factors.

Researchers have found that fidgety people burn up to low hundreds of calories daily more than otherwise similar non-fidgety people. I'm not encouraging you to fidget, just trying to illustrate that quite subtle activity changes can have a substantial impact through creeping fatigue. If that's going on, that's a "canary in the coal mine" sign that you should slow down your attempted loss rate, and maybe expect some hair thinning in a few weeks, since that can be a delayed effect.

Perceived fatigue or weakness are also danger signs, in case any of that is in the picture. (I lost too fast by accident at first, coincidentally starting that around your current weight, because MFP underestimates my calorie needs. I was then eating 1200 + all exercise calories. I was losing close to a kilogram a week. I got weak and fatigued even though I corrected quickly, then it took multiple weeks to recover. No one needs that, especially not someone with a job like yours that requires strength and energy.)

For sure, don't give up. That's really the only route to total failure. If you can improve your calorie counting accuracy, maybe work on that. (That's not a diss: Most of us doing this long term have had some "learning experiences" along the way - discovering meaningful errors or omissions. Logging is a surprisingly subtle skill. (I've been doing it for nearly 9 years, just under a year to lose around 50 pounds, the rest maintaining a healthy weight.)

Best wishes!

No evidence behind this, but having seen a lot of posts like this...
Sometimes your body just has a plateau. Think of it like setting a new, lower baseline. After a bit at the same weight, the loss starts again.
Other potential issues...
Make sure you are recording what you eat accurately. The same dish can vary widely in calories and nutrition depending on how it is prepared.
Also, as others have said, you may be eating so little that your body is slowing down and trying to keep the energy/calories.
Do your nursing shifts consist of a lot of sitting and documentation or lots of movement around the floor and lifting?