Try a really cold bath to see if that helps, just enough to lie your legs in (covered) so it's not too much for you. Some ice in it could help if you can stand it but you might find it easier with just cold first.
I used to be really active and know from things like assault courses and such I did as an RAF cadet that heavy duty stuff puts a lot of strain on your body if you aren't used to it.
Make sure you warm up and down and stretch properly as well and try and keep the exercise going without too much of a gap inbetween to get it more used to the exercise so it's not such a shock to your body. Build it up rather than going OTT. Make sure you have proper footwear as well which fits and supports you properly and is designed for impact - wearing the right footwear can make a difference.
I can't do much nowadays (more cheering at finish lines and taking photos :))but have seen friends come a huge way with their get fit regimes. From the early days of hard going training and pain in starting out they are now running charity runs, urbanathlons and all sorts, they've done so well and looking great too.
Years ago I remember turning up late to new yoga class not realising it was power yoga with a group of proper yoga snobs, an hour and a half of it later and I couldn't lift my arms above shoulder level for days, similarly my core muscles I "discovered" after my first pilates session and the riding muscles.
No pain no gain though :)