I was tested at 15 weeks as I had had GD with my last pregnancy. I think my Ob was convinced that I had preexisting diabetes and wanted to see for himself. I sort of had a suspicion that the GD was back though as I had a case of thrush (never had it before) and was peeing a lot more. It did go away however. I haven't heard of anybody yet who has had it stick around after baby was born. I had my son mid afternoon and by dinnertime that night it had all gone back to normal!
Your Ob will send you for a GTT at 6 weeks post partum which will tell you for sure that it is gone.
Oh yeah and as for the artificial sweetner thing, I had it with all 3 pregnancies and there was no problem. Also to flavour water a bit of diet cordial can make things much tastier!
Good luck with your BSLS.