Having a slight ache under my second left toe next to large toe. pain sometimes runs along the entire toe. usually felt while walking. no swelling.

Tendon/ capsule.: Not quite sure if you are talking about pain in the toe or pain in the area of the foot where the second toe meets the foot. If just the toe is involved it could be a tendon is becoming inflamed and beginning to let you know. If in the area of the ball, the something more complicated is at hand. To remove all doubt, consult with a specialist.