Thyroid conditions have caused people to gain weight, same with some birth control or medications. I would recommend seeing a doctor to rule out any issues with a possible health condition or medication you are taking.

Every time you gain weight, the number of adipose cells increases. When you lose weight, the cells shrink, but remain waiting. As a result, each time you gain and lose weight, it becomes harder and harder to lose it, and easier and easier to gain it back. This is an adaptation to protect us from starvation. At a certain point, the amount you need to reduce your caloric intake to convince your body to stop storing fat falls so low that you’ll experience malnutrition if you try it.

This is why bariatric specialists regard medical intervention as the only useful way to lose large (>15%) amounts of weight. The number of people who have lost more than 15% of their body weight and kept it off for more than five years is statistically zero, since they’re smaller than the margin of error.

You will be much better off in the long term remaining stable at a higher weight than yo-yo dieting until it becomes physiologically impossible to lose weight without causing yourself possibly irreparable harm.

According to medical charts you’re at your ideal weight (for your height), which is always harder. If you are a well-hydrated person, you can always take water pills for a week, or a diuretic to clear your bowels. Together those should drop you another 5 lbs at least short term. Cut out carbs like pasta or rice, and red meat, since they tend to stay in your stomach longer, increasing your weight. Or possibly try an all liquid diet for a week.

I’m not a dietitian or a doctor.
You know how much food that you eat in order to maintain your weight. Simply eat a little less and maintain your current activity level an over time you will lose weight.

I’m 5’11” and weigh 143lbs. I try to gain muscle weight but the more I eat the more active I am.

Good health!

@MaisyS Keto is usually something around 20 Net Grams of Carbs a day. I’ve been on it many years ago and lost 52 pounds in 70 days.
You only dropping three pounds tell me you weren’t at 20 Grams of Carbs. Some people lose 5 to 8 pounds in a week when at or below Keto levels of Carbs.

Genetics.

I am not sure why you are not losing.
I think 2 lbs per week is a reasonable expectation.
I have a 5 lb limit either way for myself (over or under my optimum weight)
When I’ve needed to lose. I have done this in a number of ways.
The first way is 1500 calories per day following the ADA’s food pyramid. I was active and my exercise consisted of weights 6x week, aerobic (any form) at least 20 min per day.
Everyone’s different, but I usually would lose 2 pounds per week. I was never hungry or tired but the pyramid way was more carb heavy and as a Type 1 diabetic, I’d have to use more insulin-which I do not want to do.
The second way I have done this is to follow any type of low carb diet. That is effective in managing blood sugars & you will lose weight rather quickly.
The third way and what I do now, is a diet geared towards managing inflammation. I have MS as well and this way of eating is fine by me.
It is a diet that is heavy on vegetables.
I manage weight with that by portion control.My exercise routine is the same as above and has been that way for over 20 years. I am strong like bull ha ha
I can be…...persnickety lol with my dietary needs and sometimes have something not in my plan but usually stick with it as I feel better.
Good luck with whatever you decide to do. :)

I would go to the doctor and get blood work done. You may have a slow thyroid (as @ashgrin said). You can get medication for it (synthetic thyroid hormone) that will speed up your metabolism. Slow thyroid has other health implications other than weight gain – hair loss, dry skin, etc.

There’s also the old “muscle is denser than fat” notion, where you could be losing fat but gaining muscle which weighs as much but has less volume, which isn’t a bad thing but does make using weight as a measure of fitness problematic.

You’re at an ideal weight, don’t worry about it. Eat healthy, exercise, maintain. Don’t do fad diets. If your exercise routine is more than normal a couple of things can be happening: you are gaining muscle mass which is a good thing, you are better hydrated which is also a good thing.

https://www.healthline.com/nutrition/20-reasons-you-are-not-losing-weight

You’re a teenager, aren’t you? Maybe your body is preparing for a growth spurt. Also, here’s a good video on why diets don’t work.

Eat more vegetables, more fiber.

Agree with @cheebdragon: genetics
I was 5’ 6” 150 lb no matter what I ate, until I hit 40. Then I had to do portion control to maintain weight.

Please re-read what @SmashTheState said. Then read it again. And once more if you need to.

Then watch the video that @longgone posted. Just don’t read the comments.

I love the title- Women are not men with breasts
“I was trying the ketogenic diet with my husband,” she told CBN News, “He lost 20 pounds. I gained weight. And I hear that from so many of my patients and my followers and I think it’s important to realize the missing piece is hormones.”
https://www1.cbn.com/cbnnews/health/2021/october/women-are-not-men-with-breasts-why-they-need-a-hormone-balancing-diet

For those of you who are offended with that title, read this instead.
https://www.prevention.com/weight-loss/a20459677/hormone-reset-diet/