I started at the same place as you. It was DAMN HARD at first!! I remember doing 1 or 2 miles on my bike and ashamedly turning around. But I was out there doing it and that's all that mattered!
This past summer I did my first 50 mile ride. It was the Tour de Peaks here in my home town of Snoqualmie WA. At the finish I laid in the grass and REVELED in the joy of having successfully completed that ride!!!!!!
I am now 50 lbs lighter and feeling sooooo muuuuuch better and it's all about getting active and eating better. Mind over FAT!!
Set some short term and long term goals and work towards them. Cycling is as much mental as it is physical. Same with diet changes.
Welcome to the active lifestyle! It ROX!!