Shin splints

Hi there! I got new running shoes ~3 weeks ago and have had shin splints ever since. I exchanged them for a different pair the other day but am experiencing pain on the inside of both shins whenever I run and pretty consistently on my right shin whenever I walk too. I’m training for the NYC marathon and wondering if/how much time I should rest for it to get better. I couldn’t run yesterday because it hurt too much. Thanks!!