My thoughts...
Plateaus, as you know, happen to many of us. I've had a few and I feel that our journeys are very personal so what I think and experience may not match what you think and experience.
The first thing to remember is that we have to adjust ourselves to a new lifestyle and that means continuing to make adjustments even WHEN we reach our goals. Saying that once you reach a plateau it is important to find out WHY things are not moving the way it was previously...saying that what I do is try to answer the following:
First set of questions: What have I been doing differently? Am I building muscle? Am I eating more food than I think? Am I eating more carbs? Am I exercising less? Am I bloated? Am I reacting to food I'm eating? etc...
For me I usually am doing something different. For example, when I start exercising my weight loss does slow down a bit. The reason why? Because I do not do it regularly(I'm still learning how to get myself moving consistently), so my body is getting used to it once again and that means I retain water. So, I have to give my body time to adjust. The other thing I notice is I am not doing what I'm supposed to be doing. Often times I'm eating more carbs and eating too much, or eating too late and skipping meals. All these things matter and I'm not one of those people who journal food or count calories. I keep things in perspective, but that is just how I do things. If you do count calories and journal your food you can look over the time period in question and perhaps see a trend or pattern.
Second set of questions: What can I do to adjust? Do I need to eat MORE calories or less? Do I need to eat more dark leafy greens, juice more, smoothies?
I think trying new things, making adjustments is important. I don't eat as much as I did when I was 340+...but that doesn't mean that I won't overdo calories. Recently I stalled and then started to gain weight back. I reached a 8-9 pound gain. The first set of questions was pretty easy to answer, I wasn't doing what I needed to, I wasn't taking care of myself basically. My body felt bad, I felt bad...so I made changes and right now am very happy. My weight has dropped significantly since Jan 1st. For me a plateau usually means I'm being self destructive, but that does not mean it will always be that way. That is just my experience as of yet. However, I do expect my weight loss to slow wayyyyy down at some point since as you become more fit things can slow down.
The other thing that I keep in mind is I'm not one of those people who can blink and lose 150 pounds in one year. I have toooooo many emotional issues that I'm working through and those directly effect my weight. The more I learn about myself the more I am able to push through obstacles. I say that because you mentioned you give up and it sounded like previously you may have been using the plateau as a reason to throw in the towel. You say you think that it might last forever, but I think there is more there. I think that is important to answer or understand. I find that when I work on myself from the inside out, I do have success. I also have noticed, for me personally, that when I just live my life that I have even more success. When I obsess over weight loss or I count calories or whatever, I tend to get overwhelmed and burnt out. I want a lifestyle change ,not a diet...if that makes sense. Changing the way I think has played an important role in where I am now.
I think also to keep in mind, and this is something I am learning, is to have patience and take the time needed to figure things out, work on ourselves, and grow.