It sounds like two things
1). you are starving yourself and your body is holding onto fat reserves to survive (it thinks it won't get fed again ha ha), but you said you eat 5/6 meals a day so don't think it's that.
2). What the girls were saying about muscle. I think this sounds spot on.
So have you measured youreself? How have you found it? Did you have a nice B.Day? Happy b.day btw

I have a spreadsheet on my laptop which had date, weight, fat %, muscle %, water %, and measurements for 2arms, 2legs, 2thighs, wasit, hips, bust. Now I haven't been good at updating it, BUT I am, only down 2 lbs in the past 3 weeks, but everyone said to me this weekend "£gosh you've lost weight", then I noticed my jeans were hanging off my bum.
So basically just cos' the scales doesn't say it doesn't mean it's not working hun. Since you're exercising, I'm sure it's muscle you have gained. How do your clothes feel? How do you feel? Do you feel more fit, more energy, more toned and happy? This is more important than pounds. You'll prob find another week later on you'll be down loads of pounds on a week you weren't expecting.
If anyone wants the spreadsheet to keep track pm me.