It could be the sweet potato - you may have eaten just a bit too much of it or otherwise it could have been what you ate for lunch, which has carried over IYKWIM. Did you have a snack btw lunch & dinner? Sometimes if you fast for too long you can then get a high reading, you should try to eat every 2-3 hrs. I would also try to do a walk after your meals to get your readings down. Sometimes I only go for 15-20 mins, slow/medium pace and this helps as it is burning sugar. I found also with yoghurt to watch which one you are having. Even if you are having low fat yoghurt, the sugar content can be really high. I have found the Valia brand really good.
If this is your first week, I wouldn't worry too much cos my GD dr said for the first couple of days she doesn't count it cos you are adjusting, but then your GD clinic sounds a bit more strict than mine. Good luck, a few of the others might have some good tips too.