I think, perhaps you should not have quit the Zoloft. Obviously you need help whether it be meds or counseling. Please realize there is help. You have felt good before and at least you realize that these thoughts are not normal. Before you jeopardize relationships and peace of mind, see a therapist. Good luck.
I actually experienced that recently. I developed general anxiety after having a series of really bad panic attacks fueled by worry thoughts. It sounds like you are experiencing the same thing. I know it sounds hard but if you can find something to pull your focus onto (i talk to my mom or boyfriend about something that is opposite of the worry) that can help lower the worry feelings.