Went through that a couple years ago training for my first tri (a 70.3).  I was told I tried to build too fast (quite possible) and needed to slow down.  I took about 8 days completely off from running and got back into it slower than before.  Stretching before and after a run, solid warmups and cooldowns, and ice were my biggest changes (I wasn't good at any of these things before my injury).  Haven't had muscle problems since.  Remember that you'll have a much better chance to finish the race if you show up to the start line.