Hi Lilly and welcome. If you´ve started to run so much only recently it may be that your muscles are retaining water - which normally goes away again after 6 weeks or so if you don´t up the intensity - but if you´ve been doing this for a longer time it would be interesting to know how much you´re eating. Healthy food is amazing but if you get too much of it you´ll still maintain or gain weight. (At the same time: you could lose weight eating burgers and fries as long as you keep the calories low, but I wouldn´t recommend it.)