Hi Claire,

I'm a 2nd Year Physio student with a background of Sports Science and Sports Massage.

You don't mention a warm up, cool down or any stretches during your weeks training.
A warm up prepares your muscles for your long runs. A cool down allows toxins and waste products (built up from the run) to be removed.

Running shortens your muscles, meaning that the muscle fibres will not be at their optimum length for your training. Stretching prevents injuries and performed regularly helps your muscle fibres to move more efficiently.

Stretching
I suggest stretching your -
Gastrocnemius, Soleus (calf), hamstrings, glutes, piriformis, hip flexors and quads. Your IT band may also be tight, so using a polystyrene roller will help.

Eccentric Exercises -
This will help strengthen your calf muscles, so good exercise.

Sports massage - I am always being asked to do calf (usually tight soleus) and hamstring massages on other students. Especially when they increased their training prior to a half-marathon. It is an effective way of stretching and also addressing any problem areas you may have...or be developing.

As for your running shoes - if you go to a specialist running shop they may be able to analyse your gait (walking and running techniques) so prescribing suitable running shoes for you. This will be a very wise investment as a correct pair will allow you to train regularly and hopefully prevent further injuries.

So my limited experience recommends -
1. Regular warming up and cooling down
2. Regular stretching
3. Buying new running shoes from a Specialist Running Shop (who can analyse your running gait).
4. Sports massage on your calf and hamstrings....if possible

Also ensure you hydrate regularly as this assists in prevention of soft tissue injuries.

Good luck ; )