IUD's are funny little things - I've had the copper IUD for about 8 months now and my body is still getting used to it. I've had a whole host of funny side effects but things are slowly returning to normal. In terms of riding - its takes some getting used to and most definitely its like breaking in a new pair of shoes - I experienced cramping while riding, but usually only within a week of my period coming or going - and after a few months I was fine. The strangest and most awkward side effect I seemed to experience was a moisture overload for the first 6 months or so...which affected my long rides, chamois comfort and there really was no way to control it - besides carrying personal wipes with the rest of my bike gear.

IUD's are great, but for those of us out there in spandex, can be a little annoying - The most important thing to remember is just to take it easy and let your body do its thing, eventually it will normalize.