Have you just lost 10lb in 3 weeks? That's brill! Well done you.
I think it's quite common for weight loss to slow a bit after the first couple of weeks, unfortunately. How about aiming for 2lbs loss each week (that's what I hope to achieve), but also setting a goal of 8lbs total by your birthday? That way if you do have a couple of 1lb or STS weeks (they are inevitable), you'll still be able to hit you goal and feel really pleased with yourself?
Plus, you'll have lost over a stone in total! In less than two months that'll be really good going.
Good luck whatever goal you decide to set. x