Don't focus so much on the scales. I have some very good scales, but they also do strange things sometimes! I have been known to lose a pound or two after a shower.
Doctor slide scales are the most accurate. Depending on how big your cups of coffee were, you may have more water weight on you than you think. I think I heard at a WW meeting a long time ago that a 12 ounce glass of water shows as a pound on the scales. If I were you, I would pick a set time to weigh, and do not vary it. You want to see fat loss anyway, not waste lost.
4 pounds in less than 2 weeks is very good for a woman of your weight. You weigh less, so your weight loss will be slower. I know it doesn't seem fair for a lighter woman to work as hard as a heavier woman, but everyone will slow down as they get lighter. Just be patient, it all adds up!
Blitz mints are sugar free. They are a UK mint, but I have seen them online at lowcarb stores in the US.