I started (again) 'get running' in August 2013 being overweight and noticing difficulty keeping up with the kids.
I was also almost 40 and the weight had crept on due to taking on a job in which I'm sat down all day and over eating.
Anyway I changed my diet, took more opportunities to walk etc. By December I had lost 2 stone in weight and was running 5k. When I started I really, really struggled with week 1.
In January I got a chest infection which turned into a nasty viral illness which has taken me 3 months to almost recover from - I've been told its post viral fatigue by the doctor. It has been really tough as this came out of the blue really and effected work, social life etc. I had 6 weeks of no energy at all - just sat in the chair. I had to not only stop running but also my main passion (other than the wife/kids) drumming in my band.
So yesterday I've gone right back to week one and got back out there and feel great for having done it. I initially felt disappointed after all the hard work from August but see it as a new challenge. Its taught me to keep on and not give up and that thinking positively can help overcome what gets thrown at us. I hope to be back up to 5k and beyond by June. If anyone else has suffered with post viral illness please let me know how you've overcome it
Don't be too hard on yourself, and do try and build it back up gradually. I completed the programme in 2012, 2013 was full of best intentions but I spent too much time bobbing about in lakes and rivers. Now I have just finished week 1 again (yay). Letting it go was the worse thing I could have done and like you I am in my 40's but still carrying the extra weight.
These viral things really seem to knock you for 6 so don't be afraid to repeat weeks but keep at it. Slowly but surely, when your body is ready you'll know and will be flying again.
Good luck. I am NOT a natural runner so I will keep staggering..