Been running 5k ish on treadmill for about 3 months. I've noticed that after half hour or so the bits of me where my inner thighs join my body get really sore -the same bits that stretch when you assume the smear test position 
. it's a muscular
pain rather than a stabbing one iykwim.
Is there a way I can build up these muscles?/Ligaments?
It's the major thing stopping me progressing to running faster or further do us like to sort it if poss.