At that weight I would imagine you could fluctuate water weight 5-15lbs. PCOS just complicates that. It also depends on what TOM of the month it is. I gain 3-5lbs the week before, but lose all that the week of. As long as the typical low keeps getting lower you are doing good. I have tried to find my triggers to holding water weight and stay away from them. My triggers are sodium and gluten. Keep going. It takes a while for your body to get going in this losing weight game, but once it does it gets easier. As learn how your body responds to food/exercise or to anything it will get easier as you know what your body will do.

I've recently taken up a high fat-low carb diet (on the advice of my fertility doctor) and for the first time ever my weight is consistent. I weigh each morning. Prior to starting this diet I would fluctuate ~4lbs every day. Now I am within a lb of my current weight.

My guess is that the insulin resistance that is the hallmark of PCOS causes us to retain lots of water, which causes these extreme weight fluctuations.

I agree with this. Pretty much the only way I've been able to avoid crazy fluctuations (upwards of 10lb in a day's time) and lose weight is low carb, high fat and Metformin. I drop one or the other and I start having issues, including a stalled weight loss and even gains (that stick) despite not really changing total calorie intake.

If you haven't recently, get your fasting insulin tested (insulin, not just glucose). I'm willing to bet that it will be on the high side (even if still in the "normal" range).

With PCOS, you basically have to throw out the window the idea that the only thing needed to lose weight is a caloric deficit. For us, especially, what we eat matters arguably more than how much. A caloric deficit is certainly necessary, but so is eating the right things (otherwise, said deficit isn't enough without going to extremes).

Eat real food -- Avoid the processed stuff as much as you can. Build your meals around meat and non-starchy vegetables, with a little fruit for dessert. This helps avoid unnecessary starchy carbs as well as a number of endocrine disruptors, both of which work against us.

Eat lower carb -- Not everyone requires a full Atkins-style ketogenic diet, but most everyone I've seen benefits from keeping their carb intake under about 150g, and a good portion do best under 100g. Again, base your meals around meat and non-starchy vegetables, instead of things like grains, and you'll have an easier time with this part.

Lift weights -- There's something about strength training in general (and in my experience, weight lifting specifically) that helps balance the hormones. Aside from that, it helps retain lean mass by keeping muscle and increasing bone density. Strength training is essential for all women, and no, you're not too heavy to start now (I've been doing it since I weighed 285).

Don't fear fat -- This is especially important if you do go low carb. Thanks to the ingrained fear of fat, most people mistakenly increase their protein when they lower carbs. This isn't really a good thing, and can be especially bad if you start dropping your carbs really low (50g or less). Protein's primary (and ideally, only) purpose is building and repairing tissue. You should eat enough for it to fulfill that function (about 1g/lb of lean body weight), and get your fuel from where you should be getting it -- fat and carbs. If you go low carb, then, you must increase your fats. That's not a bad thing, and it's not the express train to a heart attack. In fact, many people (especially those with insulin resistance) have seen dramatic improvements in their cholesterol numbers after going low carb, high fat. Carbohydrates have been pretty directly linked to triglyceride levels (which makes sense, given the fact that triglycerides are fats wrapped around sugars, basically). This includes saturated fats, and goes back to the "eat real food" part. Get your fats from real food and cold-pressed sources -- meats, avocado, olive, coconut, etc. Get the highest quality you can and avoid hydrogenated oils like the plague.

Avoid soy, gluten, and casein -- Soy is often passed off as "healthy," especially for women, but in reality, it's packed with phytoestrogens, a potent endocrine disruptor. We already have hormone issues, we don't need our food working even more against us. As for gluten, from what I've seen, a lot of women with PCOS have benefited from limiting or eliminating their gluten exposure, including helping with the "PCOS belly." Casein is a two-part issue, especially if you do react to gluten -- 1. it's cross-reactive with gluten, which means that the proteins are similar enough that the body treats it as the same; 2. I prompts a larger than expected insulin response in the body (which makes sense, when you consider that casein is found in milk, which is intended for growing infants, and insulin is a growth hormone).

Hormonal birth controls are not a treatment for PCOS -- Most hormonal birth controls are estrogen-based and work by increasing estrogen levels. This is not only not necessary in women with PCOS, but counterproductive and borderline dangerous. Women with PCOS are at risk for things like uterine cancer and endometrial issues in part because we're usually estrogen-dominant. Adding more is just putting gasoline on the fire. And no, that monthly spotting you're getting is not an actual period, but withdrawal bleed. It's wool being pulled over your eyes. That said, some birth controls, such as Yaz, are progesterone based, and have some reports of actually helping PCOS (because it helps rebalance estrogen and progesterone, and because it's a mild anti-androgen), though it carries with it its own set of issues, so proceed with caution. Regardless, if your doctor prescribes hormonal birth control as a treatment for PCOS, make sure s/he isn't prescribing the typical estrogen-based pill, knows the mechanism by which the ones that do work work, and isn't just prescribing it blindly. If s/he is prescribing the Pill blindly, get a new doctor.

Metformin isn't a unilateral treatment for PCOS, either -- Fun fact - PCOS treatment is off-label for Metformin. Really, I hope it stays that way, because not all women with PCOS even need it. Metformin is used to lower fasting insulin, and its by this mechanism that it works for many women with PCOS. But here's the thing -- not all women with PCOS are insulin resistant, not all women with PCOS will respond to Metformin, and even those that respond may not lose weight. If your doctor wants to prescribe you Metformin, make sure to get fasting insulin tested before starting and periodically while on it, otherwise, you're flying blind and have no idea if or at what dosage the Metformin will work for you. If your doctor prescribes you Metformin without testing your fasting insulin, get a new doctor.