I completely understand where you are coming from. I lost a bunch of weight two years ago, and it has slowly crept back up on me. This time around, it seems a HUNDRED times harder to lose (and like you, I'm fairly young at 22).
Remember last time when you lost that 50lbs? How amazing did that make you feel? What else makes you feel amazing? Get your hair done, get a massage, paint your toenails.... I feel it's a heck of a lot easier to get motivated when I feel good about myself already. Self-loathing is not going to motivate you to make yourself better. Focus on something other then the weight you need to lose for a while.
I try to do something everyday that makes me feel good, besides eating healthily and working out. Even it's something as small as keeping my legs shaved and putting on my favorite (and a little bit expensive) body lotion after showering.
Make you're doing some physical activity that you ENJOY. If you hate what you are doing, you won't keep doing it. If you love hiking, have at it.
On the same note, make sure that you are eating food that you love. Now, that doesn't mean to eat a whole jar of Nutella (note to myself..
), but you can't force yourself to go from a diet full of junk food, to eating only steamed vegetables everyday.
Good luck and stick with it!