Nikki, welcome to"our"world. First of all, a combination of mild running and walking at first is a good combination. the idea is to build up strength gradually, in your ankles, shins, calf and thigh muscles. If you are going to run properly, i strongly advise you to invest in a pair of decent running shoes by going to a running shop that and if they have a footscan system, all the more better. Try to run outside as well rather than in the gym on the treadmill, as the treadmill's pace is non adjustable to your running speed, hence you maybe out of steam before time and the fact that when you're inside it gets hot and boring. running outside helps your leg development muscles as well as your lungs and stamina, as all roads have different inclines and the fact now that we have beautiful weather, it feels better too! Increase the mileage month by month say from 2m to 3m and also initroduce some kind of a session work i.e sprint or hill climbs with reps. This session helps you with your running speed and efficency. Keep up the good work!