I was always skinny until I settled into my office job. I got up to 220lbs at 6'0". Not fat? Hardly. 25% BMI.
You can rationalize anything until you look honestly at yourself naked in the mirror.
I did and then asked myself if I wanted to be a fat guy or not. Being lazy by nature it was an honest questions. I seriously weighed the pros and cons of being lazy and fat (more time for video games, less pain, etc) and healthy and fit (working out, not eating whatever I wanted, etc)
My decision ultimately was, "NO! I don't want to be a FAT GUY!"
I got a personal trainer to teach me how to work out and lose weight. I got free weights and an elliptical. Get sensible about what I ate. And I'm a trim 185lbs now.
The best thing is the sex. My wife loves my hard body and literally can't keep her hands off me. It's better than when I was skinny because the muscles turn her on, and frankly me too. I'm still a little surprised in the shower when I soap up my shoulders because they're so much bigger than I'm used to.
Make yourself a 12 week commitment for a better body. Eat right 6 out of 7 days a week. DO an HOUR of cardio every day. Treadmill burns the most calories, but I think eliiptical is almost as good and is certainly easier on your joints. And lift weights to build muscle. Muscle BURNS calories so bigger muscles mean faster fat loss.