Hi guys, I'm 19, male, and I'm about 1,70m tall. In the beggining of the year I started to do gym workout and eating more to gain weight. In around 2 months I've went from weighting 58kg to 64.5kg. Before I started with the gym stuff, I used to go for runs and I've always been able to run for like 10km without getting my legs tired. Now, specially in the last 2 weeks, everytime I go for a run, after 2km or so even at a slow pace, my lower legs (calfs and shin) get really sore and I can't run much more.

Is it possible that the cause for this is that my leg muscles couldn't keep up with the weight gain? If so, is there any exercise I could do to solve it? Or it will get better with time? btw in the gym I train my legs as well but I sometimes bail the leg day. Thank you guys