Good morning.
I know it seems to be the buzz word of the moment but maybe you have a weak core?
If your core is weak, you use other muscles to stabilise your body. These muscles weren't meant for this purpose and so end up getting tight and causing problems.
If you go to a gym, ask an instructor to show you some exercises to strengthen your core and generally strengthen your muscles (exercises using several muscle groups at once are best eg squats and lunges) and get him/her to ensure you are doing them correctly. Also pilates classes are good for working the core and helping stretch tight muscles - I know I always feel taller after a pilates class but I guess that is probably more psychological than physiological.
It is best to combine running with strength training and flexibility work eg yoga as Hoose suggested. All elements need to be worked on to keep you running injury-free.
Also doing other aerobic type exercise as well as the running will help - swimming, cycling, using the elliptical trainer in the gym - as these have less or no impact on your joints.
Good luck with it.