i've never understood this mentality, how many of your waking hours are spent eating? is food the only thing that gives you quality of life? think about how your body feels the other 22-23 or hours of the day, is it worth it for the hour or two of "happiness" that eating junk food gives you?

i think one problem is that you cut out everything too quickly. being healthy and fit requires a lifestyle change, and quite a few people find it more beneficial to take small steps toward their goals rather than just quit all unhealthy eating habits cold turkey, which often leads to binge eating.

focus on cutting back a little bit at a time, at first you may not feel like you're making much progress but over time it gets easier, and one day you'll wake up and realize you no longer crave all the junk you did before. trust me, i've been there, and i'm glad to say that i'm finally at a point in my life where i no longer crave sodas, candy, fried food, etc. in fact, looking back on it i don't see how i could have eaten that junk to begin with. i still have the occasional unhealthy snack, but it's usually one or two a week, not one or two a day. you mentioned how much you ate when you were 18, i ate that much and more and it was nearly impossible to gain weight back then. but as you get older you'll find it much easier to gain weight and harder to keep it off.

it may help to put your goals down in writing. maybe your goal is to get down to 110 lbs, or be able to ride 50 miles, or run a half marathon. think big, and then plan out intermediate goals that will work you towards that end goal. you might also subscribe to a magazine like Women's Health or something similar. this has helped my wife a lot, just having that magazine around to read every now and then motivates her to eat healthier and get more exercise, and there's lots of good exercise and diet tips in there. but really, the goal should be to live a life that makes you happy. you're obviously not happy in your current state, so you have to decide what makes you happier... junk food for maybe 1-2 hours a day, or being healthy and fit 24/7? it's possible to have a balance of the two, if you still want to eat junk food try to do it in moderation. but trust me, once you start taking those small steps toward healthier eating habits, it'll become much easier than you think possible.

it's well known that exercise and being fit can (and usually will) also improve your mental state and self-confidence. i got depressed when i gained 20 lbs in less than a year, and it took me a while to reverse my bad eating habits and get into a steady workout routine, but one bit of advice i'd have for you is to find a way to make exercise fun. for me, it was cycling... i really enjoy it, and it just so happens to have led to me losing 15 of those 20 lbs in just a couple months. we have an elliptical at home, an expensive one at that (more expensive than my road bike), and i still use it once or twice a week, but i can't get on that thing every day. i feel like a hamster in a wheel and get bored easily, so i go for rides anywhere from 3-5 days a week, and when i can't get outside i'll do maybe 20-30 minutes on the elliptical.

as for your endurance, just keep at it and it will improve. when i first got on an elliptical, i could only go about 5 minutes before my legs were on fire and felt like they just wouldn't work anymore. same with a bike, i could only go maybe 5 miles before my legs wanted to give out on me. now i'm riding at least an hour each time i go out, maybe 3 days during the week, and closer to 2 hours on a saturday or sunday ride.