Hey Pop,
You sound like this is upsetting you a great deal. It is good that you are going to see your doctor today. I was just reading about the side effects of Zoloft is changes in weight. So it is more than possible that Zoloft is causing your weight gain so it is good that you are talking to your doctor about this. Keep in mind though Zoloft and Lexapro are both in the category of selective serontonin reuptake inhibitors (SSRI's) so they MAY both produce the same results.
I was on Zoloft for a few months and I too gained weight. I have OCD as well so I know all about racing thoughts....it STINKS! Also, I have always been what I consider borderline eating disorder. I am currently on Lexapro and I find that it has helped a great deal with the OCD. However, I have gained weight with this too. But for me I have gained weight because of my change in appetite/ Premedication me was SEVERELY panic ridden and Depressed, etc. but VERY thin. Post med me has gained quite a bit of weight. However, I am much happier! And I do find that I can lose weight when I stick to a healthy eating regimen and exercise. So I think for me and for many other people when you have Anxiety or Depression and are not medicated you tend to not have an appetite at all hence you are much thinner where as when you start taking medcation to quell these disorders you tend to naturally be much happier and your appetite increases with it and if your not careful your weight too. Now with that being said, to me, it DOES NOT sound like this is the case for you. So good luck with your doctor. You and he/she can discuss your possibilites with medications and/or counseling which is in addition to medication is a key component to getting well.

Jennifer