Try not to be too down about it.
The amount of weight you lose on a weekly basis will probably fluctuate quite a bit based on a lot of factors (hormonal changes at different times of the month, sodium and water intake, changes to the balance of carbs/protein/fats - a LOT of things), and I think that's pretty normal.
I saw a nutritionist last week, and I took to my appointment my entire food log from the past ~2 months, my exercise log, and my weight log. She pointed to the week when I lost 'only' 1.4 lbs and said "what happened that week?" Nothing special happened that week - I ate within my calories, I exercised, etc. I just didn't see a big drop that week.
It was, however, followed by a week in which I lost a huge amount (5.9 lbs)... so there's definitely hope that you'll see a bigger drop at your weigh-in next week.
Keep doing what you're doing right now, as it's clearly working - you are losing weight! It WILL come off, and you'll see patterns and find strategies along the way that will help you to maximize your loss while staying healthy. Good luck, and stay positive.
Btw, I am totally impressed that you can run two miles. I struggled this week through Week 1 of C25K, which involves only 60 seconds of running at a time, lol. Congrats on all the progress you have made so far - it really IS an achievement.