I was in a similar situation to you at your age (I'm 36 now). I can't say that the following is what the "experts" would advise, but it worked for me.
IMHO, there is one, and only one way to lose weight. That is to expend more calories than you consume. In other words, eat less, and exercise more.
To lose weight, I cut out all desserts and all in between meal snacks (some would advise that healthy in between meal snacks and smaller meals overall are actually better for you - they may be right - I'm just telling you what worked for me). And I mean I cut them out completely. This was, of course, not easy. You really need to change your way of thinking. I also tried to select healthier things to eat. This is also not easy. At your age, you are probably not often in charge of your daily menu (at least not your dinner menu). However, I would at least see about eliminating all of the unhealthy snacks and drinks from your household (if no one objects, throw out the cookies, cakes, sugared soda, sugared juice drinks, etc.). If you're hungry, have a piece of fruit instead of a cookie (I've been eating fruit for so long now in substitute of more fattening snacks, that I actually prefer it to most of the high sugar or high fat foods). One trick I used to avoid eating desserts was to always have a cup of coffee when everyone else was eating dessert. I found this to be a way to keep myself busy while others were eating, and coffee has zero calories.
Further, you need to practice portion control. You don't need two sandwiches at lunch - you only need one. If you must have them, don't sit down with an entire bag of chips in front of you. Pour a small amount on your plate and put the bag back up on the shelf. At dinner, you don't need that second piece of bread, second hot dog, or a second steak. If you go out to eat (where portions are often huge), don't be afraid to leave a little on your plate (whether you decide to take the rest home or not). Give your body time to realize it's eaten. You'll feel satisfied without the larger portion. Also, I don't know if you drink, but alcohol has lots of empty calories.
One other piece of advice on eating - don't ever go to the grocery store on an empty stomach. You'll end up buying all sorts of fattening crap that you don't need instead of what you should be eating.
As for exercise, find something you enjoy and stick with it. For me it was some resistance training along with some cardio (generaly riding an exercise bike). I still make it a part of each day. Don't do something you hate doing, because you won't stick with it (for me, this was running - I loathe it). Set aside a prescribed time every day to exercise. If you just go in with an attitude of "I should try to exercise every day," you won't do it. You need to make it a part of your permanent schedule. If this means getting up an hour earlier, so be it. Again, this is not easy. You need to be committed.
The last thing I would advise is be realistic. Above, you talk about losing 85 pounds in 5 months. That's a lot of weight to drop in that time period (regardless of what the fad diets and/or television may tell you). Be happy with your short term gains, and don't get worried if you plateau from time to time (it happens). You generally will lose a lot of weight up front (similar to the experience you post above), but you'll slow down after that. Just take it nice and easy. Understand that this is a life long battle. I went from about 260 lbs to about 185 pounds (I'm 6'2"). It took me several years to make this change (I started around 1988 and finished around 1996). I probably could have done it faster, but I wasn't in any rush. For most of this time period, I probably weighed between 200 and 220. I made the final push down to 185 after I graduated from law school (not so coincidentally, this is when my drinking cut way down, since I wasn't going out every Friday and Saturday night anymore).
I guess the final thing is that, from my experience, the weight loss was definitely worth it. It does wonder for self-esteem. I found myself more confident in talking to people (especially women), and I experienced a lot more success with the opposite sex. Good luck!