I started cycling to work 3 times a week about 2 months ago!
Was great to read through your thread teen as I've already been through several of the 'humps' you found - wanting to collapse, sore arse, getting better etc!
I'm cycling to work (6.2 miles each way) 3 times a week after not being on a bike for 15+ years! I was slightly overweight before - 14.5 stone, I'm 6'7" and always been fairly heavy set. I'm finding it much easier now, but all it takes is the wind to blow the wrong way and I struggle! Cardio is my problem now, my stamina has always been good - I can keep going until I feel dizzy!
I've not taken a look at the mapmyride website yet, but how are you plotting things? Got a GPS device of some kind and heartrate watch etc?
Would be good to find a nice easy way to check my progress - I'm too busy to cycle for recreational purposes, but for work it's quicker than my car (on the way home).
I've lost over half a stone already, not changed diet and don't really have any other regular exercise... Not sure if I'm enjoying it yet, as didn't start until the cooler weather (to help stop me overheating!) and I've got soaked a few times!