Exercise! Start out by walking a lot. Go on afternoon walks if the weather permits. It clears your mind, and begins to get you healthy. Once you are comfortable with those, move on to running and other types of exercise (i just love running, haha).
And, you said you're only 18 years old. You have absolutely no way of telling where your life is headed at this point. I bet you're a senior in high school, meaning you have your entire life ahead of you. When you get out of high school, your friends change, the people around you aren't as immature and judgmental as they were in high school.
To find love, honestly, just be yourself. Someday, you will find someone who loves you for you, and doesn't give a care what you look like. If you are truly yourself, you'll be happy, and my guy friends all seem to agree that they'd much prefer a girl who is happy, and themselves, than anyone else.