o answer your questions, I have started to swim again, but I am the least worried about this leg. I was a competitive swimmer in high school and an ocean lifeguard through college. The run on the other hand terrifies me, especially for the second race - I have never run a 10K in my life, much less after swimming and biking.
You sound just like me!

I was a competitive swimmer in H.S. and it's truly a skill you never lose.

I typically zoom through the water and place 1st or 2nd in my age group for the swim portion.

Then I bike... and I average around 18 MPH, so I do pretty good at holding my own on the road.

Then I run. No wait. I walk and run... get a side cramp... double over... pinch my side... have a funny little jog hunched over... that brings me in on an 11-12 minute mile. Which I am quite proud of, considering.

After my tri season last year, I decided to train for a 1/2 marathon, to get over my "I can't run" fear/thoughts.

I trained for about 2 months, and then I got leg pain. Not sure it was the achilles (?) tendon, shin splints, who knows. I had to give up training.

Took time off, and started to run a little bit again... and BAM the leg pain is back. So, I have changed my running form, I walk/run, and I am working on uping my miles... but the leg pain is still there and very painful (it's not a physical injury, the x-rays came back clean).

Anyways... I went off on a tangent. I wish you the best of luck in training for tri's.