Need HELP!!!

ToNiBeE99

So, I am training for a half marathon in November. I'm using an app to train and I run 4-5 times a week burning 300-1200 calories/run. I don't lift weights but I do want to start in a week or two. My calorie intake is 1400. In a month I have lost 20 pounds. I'm going on week number 2 staying at the same weight. I don't know why I'm stuck? Do I need to increase my calorie intake, am I not eating the right foods? I just don't know?!? Can anyone help me with this delay. Thanks.