Very frustrating

First unofficial marathon for a while managed a very comfortable pain free 3hr 30mins, within an hour of finishing i could hardly walk, my groin/pelvis area completely seized up, walking in a straight line was OK but any attempt to change direction was very painful, the discomfort stopped me sleeping so i was up early on sunday and went for a gentle cycle (as you do when you can't walk) to loosen up my legs, seems to have done the trick, not exactly pain free but at least I'm not limited to walking in a straight line, couple of days off now so going to concentrate on stretching at every opportunity to see if that helps..