
We're doing the Peterborough half on the same day (except we've just got an email to say there was some SNAFU with them taking payment for our entries). Am v jealous of you doing Royal Parks, it's a lovely event - I got my PB there last year.
Sounds like your training is going fine. 10 miles is a very long run to do at this stage - is that the longest you're going to do? What programme are you following?
Re the headaches and tiredness, my totally unqualitied layman's view is that you need more salt. You can make an isotonic-type drink with orange juice, sugar, salt and water - not tried it myself but apparently it tastes fine. Or obviously bought sports drinks contain salt, or just eat a packet of crisps! Should help with the fatigue too, a bit.
We did our marathon training last year in Jan/Feb/March and I was amazed how cold I found it. I'd wear tights, warmer trousers over those, a long-sleeved top, a gilet over that, a jacket over that (which I'd take off if I got too hot) and a headband/scarf thing and a baseball cap, and gloves. And I am not someone who feels the cold badly at all! I didn't wrap up to quite this extent for shorter, faster runs but for the long slow ones I found I needed it. Your hands get terribly cold, and I found my hips got really sore if I wasn't wrapped up warm in the arse area 