You're doing great!! Def keep at it!
It took 25lbs for others to see a difference and myself, although even at 25lbs I don't notice much (haven't gone down a size and nothing fits super loose) but when I wear things that were tighter before I can feel it and then see it.
I know it's frustrating though bc really 18lbs is a lot of weight but before you know it's going to show! I've been taking measurements and pictures every 15lbs so I can see a difference! (I wanted to do 20lb but that was taking forever!)
I remember reading this quote somewhere Im going to see if I can find it and link it on here!
Found it!
http://3.bp.blogspot.com/-Gv8ryGTUYx...-12-weeks2.jpg
I know this is going by time (versus weight) but since you're 3.5 weeks in I'm sure you'll notice come 12 weeks!