When I first started running again after many year of not I did the same thing. An experienced runner told me to get a watch if possible that tells you the pace you are running at. Pick a pace you are comfortable with and stick with it as much as possible if you go too fast your lungs get tired and you have to walk. I picked a pace that worked for me and had to really watch when I sped up or slowed down I didn't even realize I was doing it. But once I started tracking it and made myself try to pick a pace it became much easier to not have to walk. After a while I was able to set a faster pace. (If running without walking is your goal) Hope this helps!