Whoa, I do not recommend circumcision. If you read online, most people who have to get circumcised at a mature age are very unhappy with it. Many of your nerve endings are towards the top of your foreskin and sex will feel much LESS enjoyable. Many people either feel one or the other so they do not really notice, but those who get circumcised later on in life end up regretting it. Just look it up on the net. And yes, there is a name for it and yes, there is the word disease, but it is not a life threatening one or uncureable. DJBen knows what he's talking about with the stretching. I had to go through it too when I was a teenager, I never retracted when I was a kid growing up and eventually I realized something was wrong and read up on the it on my own because of embarassment.
Basically, you just start pulling back little and little. Just as far as you comfortably can. Doing it in the bath is good too. If you've never done it before, there will be smegma, a white creamy substance. Once you can fully retract it which should take at least a few weeks to a few months, you can clean that off every day when you shower.
If you do get circumcised for whatever reason, it is not sensitive for just a week or two, it's sensitive for a few weeks, heading towards possibly a month or even two. It will get irritated rubbing against clothing and underwear. If you and your girlfriend do not have a problem with it, then I say your best bet is just stretching. Getting skin cut off your penis is a very big step with very dramatic drawbacks.