Hi Mandy!
I agree with LesGetFit. You are young, you have a gym, and although 51 lbs to lose may seem like a lot, it can go very quickly when you put your mind to it! I'm 54 and I've lost 40 lbs since May, so if I can do it, so can you! Don't do any crazy fad diets though, and be prepared to continue eating healthily and exercising after you lose the weight, because the weight comes back on more quickly than it comes off, and if you think you can diet and then just go back to poor eating, it will come back on and then some. You have to be committed to changing for good the way you've been doing things. But you have everything going for you, and I know you can do it! So just jump in and start posting! People are very friendly and non-judgmental here! Some threads are more active than others so just check the dates. Good luck!