Minor calf pull 3 weeks before IM !

Assuming that this is actually something musculoskeletal and nothing else, your best bet right now is ice only for the next 2 days.  It will slow down the rate of cell death and can help prevent edema.  Inflammation is a normal response but you need to keep it under control.  Medication wise, acetaminophen (Tylenol) over the first 1-2 days, then Advil or Aleve after that.  Stay away from aspirin or Excedrin.  You can use massage/foam roll your hamstring/calf, AWAY from the injury site to help prevent muscle spasm, and if you have access to a portable stim unit you can use that to help with pain as long as there is no muscle contraction involved.  ROM exercises without weight will help as long as they are painfree and you can start those immediately.  I'd say for the next 5-7 days stay off the bike and run training and hit the swim...you can still train without putting stress on your calf.  Once you can walk and do ROM exercises with no pain, start with easy strengthening like calf raises (2 legs, then 1 leg), step ups, step downs, lunges, etc.  Once exercises are pain free then you can get back on the bike.  If the bike doesn't hurt, get back to running.  Short distances only at first, progressing longer, again, as long as painfree.  If you need to walk, walk.  Don't push through it and aggravate it.  Keep icing your calf at the end of every workout for 15-20 minutes, and it wouldn't hurt to do that all the way through to the race even if it feels fine after the workout.

One thing that won't help is complete rest followed by running again.   

I've been getting the same thing, repeatedly.  I'm just getting started and have put run training on the shelf at least three times in the last six months waiting for this thing to recover.  Thanks for the advice on how to treat it.  Do you know what causes it?  Like I said, I'm a beginner and I'm not great at staying hydrated (I love the diet cokes).  Also, I've been using trail running shoes to run on the streets.  I have been starting slowly running 60 sec then walking 90 sec for approx 25-30 min.  

What can I do to keep this from happening?