Sounds like shin splints, which you will find loads about on google.
you should rest, look up R.I.C.E.
usual things to help are calf stretch exercises, you also should have your running shoes checked at a proper running shop. I found over pronation was causing mine, now I have the right shoes I have no issues.
hope it all works out for you and well done on your 3 miles, I remember feeling very pleased when I got that milestone.