Reaching Plateu's on Weight loss journey!

You haven't really given us enough information to give you nuanced advice. Do you have an active or sedentary job? What is your 5 days of gym exercise, for how long do you workout at each thing? Did you change your workout type/intensity/frequency sometime close to the start of the weight stall? How long did it take you to lose the 16-18 pounds? (I'm even assuming you meant pounds, not kilograms.)

If a person has been losing at a pretty good rate, keeps up the same eating/exercise routine, then stalls suddenly, higher odds the issue is water retention, or a change in eating patterns that changed the average amount of waste in the digestive tract. Healthy bodies retain more or less water for a huge number of reasons, and it can vary by multiple pounds from one day to the next, and can hang around for a surprisingly long time sometimes. When that happens, it hides fat loss progress on the scale.

Some possible triggers for increased water retention:
* Cutting way down on carbs at the start, then creeping more of them back in. That's not fat gain, it's that our bodies need more water retention to metabolize the carbs. It's no big deal.
* Losing very aggressively fast at the start, and trying to stick with that ultra-low calorie level. Loosely, that's a physical stress, and stress can increase water retention.
* Injury or illness.
* Hormonal level fluctuations for women who have menstrual cycles.

Read more here, 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

None of that is about fat loss, so the solution is to understand and expect it, not to try to game it. Fat loss is what we're really going for, isn't it?

On the opposite end of the spectrum, if someone has been losing, and the loss rate gradually slowed down then stalled, higher odds they've found their maintenance calories. I have to say, 16-18 pounds wouldn't make a huge difference in calorie needs all by itself, but that plus reduction of exercise calories or a major change in daily life routine could do it.

If you're in the "stopped suddenly" scenario, the answer honestly is to just stick with the routine that was triggering a good weight loss rate previously, and your body is likely to deliver results, just on a delayed basis. Well, if you've been losing fast previously via that "ultra low calories" thing, don't keep doing that. It's seriously not healthy.

If loss rate was a gradual slowdown then stop, then reduce calories by maybe 250 or so per day, and see how the trend looks in 4-6 weeks at the same calorie and activity level.

If your 1200-1500 calories is accurate, and a consistent average, I'd expect you to be losing weight. Your profile says you're female, you're 31, your profile says you're in the US so we'll assume 192 is pounds, you're 5'7". We'd expect your BMR - the number of calories you'd burn flat out in bed in a coma - to be around 1600. If I assume your job is fully sedentary, but you gym 5 days a week, your total calorie needs (TDEE, total daily energy expenditure) would probably be 2200-2300ish. If you're statistically average, we'd expect you to be losing a pound to a pound to two pounds per week. (If you're shooting for 2 pounds a week, I'd encourage you to slow the bus down.)

If you're calorie logging, and especially if you're new to it, it can be a surprisingly subtle skill. Most people underestimate calorie intake, even when logging carefully. Be sure you're logging every bite, lick, taste, cooking oils, beverages, condiments, treat/cheat/oops days, etc. If you want experienced people to look at your diary and see if there are any things that jump out there - things that tripped us up when we started - then open your diary to MFP public, and tell us you've done so. That's an offer, BTW, not a demand.

Changing workouts isn't going to do anything, unless it reduces water retention from less muscle challenge (maybe not good for other reasons), or burns lots more calories (which is unlikely, since the contribution from exercise calories is relatively small for most of us). Over-exercise isn't good because it can reduce daily life calorie burn through fatigue, so that may be a diminishing return . . . and I think you might want to consider focusing on developing healthful habits that will give you a happy, healthy life long term, rather than focusing on fast loss, since it's nice to stay at a healthy weight forever once we get there.

Drinking more water won't do much either, unless it relieves constipation, breaks loose some retained water, or helps you stay more full so sticking with calorie goal is easier.

HIIT, specifically, is very over-hyped and over-rated these days. It can be fatiguing, create more injury risk through fast pace and less well-managed form, and more. Unless you love it, why do it? I'd strongly suggest finding a healthy, enjoyable (at least tolerable), practical exercise activity routine, then picking a suitable, sensible calorie intake for that routine and your goals. Exercise for health more than weight loss, would be my advice. That we get to eat more while losing at the same sensible rate is just a nice bonus.

If you made me guess, I'd say the best answer is make sure your logging is on point, then stick with your current routine patiently for a few more weeks. Patient persistence is a very real part of success, IME. If you can make your goals be about process - logging daily, doing planned workouts, etc. - rather than about what the scale says over a day or week or whatever, that IMO will increase chances of success.

Best wishes: Success is out there.