I would say that is a fair amount of exercise, you may want to try doing things like intervals within those miles this way you don't plateu. 10 min mile is okay for a cruising speed. For reference most collegite/high school girls run the mile around 5 or 6 minutes. But distance is all about miles, some collegite athletes put in 100 miles a week.
Now if you were to run a 5k it is not 5 miles, because 1000m is 1k and 1600m is 1 mile so a 5k is somewhere around 3.2 miles I think(it's kinda early and school hasn't started so my math isn't on point). Hope this helps.
Young people can get away with running everyday, but the older we get, the worse idea that is, especailly starting out.
It can take a while to see changes in your body. You don't necessarily loose wieght and inches proportionatley, or even at the same time. Yes, you can build muscle from running. But I'll bet you feel better already.
The best way i have found to build up fitness through running is to have something to aim for. A friend recently recommended www.runlondon.co.uk , it's all about Nike run london which is a 10k run but this year there are also a series of training runs across London making it an all year round event. The site has got some great training ideas for all levels of fitness also so you can add a bit of interest to your excercise. It would also help you to measure your progress which it seems is what you're struggling with. Check it out and give it a go, Good Luck!