Okay, so you have been at this for 8-9 days, since today doesn't really count yet.
You just started exercise so you might be carrying some water weight around. When I change my exercise pattern it usually takes 1-2 weeks for the water to settle down. Someone told me once that if your muscles are sore you are retaining water. Don't know if that is true, but it has always seemed true in my experience. (Case in point, I ran a mile extra yesterday, am up two pounds this morning, my legs and shoulders ache...)
Do I remember you saying that you have a HRM that gives you calories burned? How many cals are you burning each day from exercise? I think you said you netted around 850 every day after exercise calories? My first instinct would be that your calories are too low. But, I would give it two weeks on plan to see.
You mention some days under, some days over, some days on plan. Did you average 1350 for the whole time or did the over plan days move you up some? People will tell you to be careful and not go below 1200, also - I noticed when I got below 1200 consumed on any day in the week I didn't lose any, even if my average for the week was higher.
So, long answer, short summary. If it were me I would give it until 1/16 -that would be two weeks. If you haven't lost by then I would actually try increasing the total calories consumed a little - 50-100 per day maybe? Also, a rest day is important - your muscles need time to recover. I had to make sure to take one day off per week, sometime two if I was really sore, of my loss stalled also.
ETA: oops, didn't notice the forum, just the title... I'm not actually a 20-something, I'm 36...