I cant stress this more, GET A HEART RATE MONITOR!!! I bought one, read about the fat burning zone (lots of different opinions about this but between 65-80% of your max heart rate) and stick with it. When I started riding I thought no mater what, keep pedaling, I'll lose weght but I wasnt (or it was very slow) then I learned about how your body uses fat for energy and now I'm getting fitter and losing weight.
Whats funny is, if you stay in this range, you may very well feel like your not working very hard as most of us think you should be out of breath or your heart should be pounding in your chest or sweat should be pouring off you but thats not true to burning fat. Stay in in your fat burning zone for about 2-3 months and you'll see a BIG difference.
By the way, well f@#*^ng done for doing this, it takes great dedication to lose weight, well done mate! keep posting and good luck, we are all here for you