Here to lose weight

I am Brandon and trying to lose atleast 50lbs to start. I've lost it before, but gain it back each time. I would like to lose atleast 25lbs by thanksgiving when I go home for the holiday. I enjoy stationary bike, sit up machine and the elliptical. I have a vein I have to be careful about so I need to lose weight to help with them and make sure I don't get diabetes. All encouragement and tips is welcome