That's fairly common though, you are putting in plenty of miles on a regular basis, and it will build up a standard speed per mile. Running does become quite addictive, and is a great way to clear the mind too.
Agree on both counts - I've got a massively addictive personality and keep getting addicted to running before something or other happens. It's been injury in the past, simply through over-doing it. In the Summer of 2013 I'd really been getting into my running and intended to carry on when I went off to Florida on holiday. I didn't however and just stopped completely as other life stuff took over.