I went when I was about 5 weeks. Again they didn't do anything, just made a note in my file I was pregnant and the dates and that was it.
Told me to book in with the midwife from 8 weeks onward and it would go from there. Saw her at 8 weeks and she said they normally didn't worry about any appointments till nearer 12 weeks but it was ok to come in early. Again nothing exciting, just paperwork.
TBH there is nothing they can do for you in the very early stages other than let nature take its course, so unless you have problems, I'd be inclined to not worry seeing the MW until at least 8 weeks, but it won't hurt to let your GP know you've had a positive pregnancy test and they will make a note of it or possibly do another one for you to back it up.
But then each GP surgery is different, so always best to visit them and see what their policy for it all is.