Snow puddles: there are a couple things you may want to think about when it comes to factors affecting your weight. this is going to be kinda long...
1. how much are you eating? if you were to track your calorie intake how much are you coming out with....you may be taking more than you think OR taking in LESS and i mean way less than you think. I personally struggled with this when I was in my teens...the whole eat less to lose weight concept really failed me and although I worked out like crazy, i gained weight because i was eating a lot less than my what i needed to lose...
I'm still learning about metabolism myself, Here's the little info I know about metabolism...
A) you shouldn't eat below your metabolism when dropping calories (so if you calculate your BMR and you get 1300 or whatever, then you need to eat at a MINIMUM that or above HOWEVER
when you're as active as you are your Daily Calorie Expenditure (this is your BMR + lifestyle activities + intentional physical activity) should be higher. So say that you're BMR is 1650 + another 400 for lifestyle activities (i.e. attending school, chores, errands, work, etc) + 500 burned during each session of your run = 2550 to lose a 1 lb a week - 500 (2050) or lose 1.75-2 lb a week -800 (1750). Try not to create deficit larger than 1000 continuously as it may cause you to lose muscle mass, every once in a while or once a week shouldn't do much damage.
When you determine how much you need to eat to lose, i suggest varying your choice of food each day if possible and how much you eat (so say one day you eat 1650, next day eat 2000, next day eat 1700, etc) and also varying your workout a bit too. I'm not sure if doing 5 miles one day and 8 the next may be enough of a variation as your using the same muscles? however including some other form of cardio into that routine and the sugg. on the diet would keep your metabolism confused...the same routine after a while allows your body to create an adaption so you're no longer challenging the body and that when you plateau and stop losing weight or seeing effects from your exercise/eating....<this is the part that I'm still working to understand in detail, so if you come across something, you should post it>
Plugging your info into fitday may be helpful (in terms of how much you burn) and if fitday doesn't aide in finding the foods you eat, track it by manually writing it down or using other online programs
FYI: when you calculate your BMR on fitday I would suggest using the Mifflin...it took me a while to finally realize that its' the most accurate or closer than Harris Benedict...I'm not sure how other's have done it.
2. similar to the previous response; running is weight bearing and perhaps you be gaining some muscles. I used to run about that much 5 days a week 5-8 miles per day and only worked out my upper body strength...and I felt firm...like lean firm.
3. in terms of a device that you can use to accurately weigh yourself, I would suggest a digital scale...with the function of a fat % /water/body mass. While these may not be accurate to the T, they can still tell you when you have more water weight, vs. more muscle %, you get the idea?
Here's one that I own: Full Body Sensing Body Composition Monitor and Scale with Seven Fitness Indicators - Bed Bath & Beyond
it's a bit more than most people want to pay for a scale but I like it. and if you go here you can print out a 20% coupon Bed Bath and Beyond Coupons - Find Online Coupons & Discount Codes for Bed Bath and Beyond
or if you have a bed bath and beyond store close by you, they display these sometimes so you could go in there like...once a week and weigh yourself :~)
4. How are your clothes fitting? are they looser? tighter? good indicator of weight loss. When I start doing any type of weight bearing activity, I start to feel bulky/swollen im pretty short so it's not a feeling I like, but then when I put on my clothes and all is well...it's encouraging.
I hope other's continue to post informative feedback on here for you...in the mean time, research your question and you'd be surprised what you can learn and share with others...