Why do my shins hurt?

In December I started having pain in my shins when I ran. I went to the doctor who said it was going to develop into stress fractures if I didn't take time off. I don't run much though so it seems odd to me that it would be stress fractures. I took about two months off and I was fine when I ran occasionally but a few weeks ago I started running more often and I am feeling pain again. Sometimes it hurts the next day hen I walk. Is this stress fractures or shin splints? And how can I treat it?