3.5 lbs is a good loss over 3 weeks, I always remember a loss is a loss. SW do say to expect losses of 1-2lbs a week, which is healthy.
If you think your sweet tooth is having an effect - then unless you can control yourself to have a certain amount within your syns, I would suggest to to get rid of it! Find low syn or syn free things instead to satisfy your cravings. Don't deprive yourself completely of treats, as that's when you'll fall off the wagon.
As for motivation - think about why you joined SW in the first place and write down the reasons why you want to lose weight. Please don't lose heart - you've lost weight so far which is brilliant and an hour on a bike a day is great exercise!
Keep going!
ETA - Just saw you're doing EE - are you making sure 1/3 of your plate is superfree food (fruit/veg)? Also make sure you're weighing healthy extras - don't guess the amount!