I've started getting pain near the bridge of the foot when my toes are bent up, esp with yoga standing strength or plank poses. what have i done?

Strain plantar fasci: You have possibly strain the plantar fascia. I believe you need to stretch your plantar fascia area of your foot ( which is the bridge of your foot and toes) Rest your foot for 3 weeks,( so no yoga during this time period).If after resting your foot for 3 weeks, if you do not feel any better then you should go see a doctor who specializes in foot an ankle.

Prob. chronic strain: Perhaps strain/'chronic sprain' of the extensor (front) fascia of the ankle joint. Or similar process affecting ligaments of the midfoot bones. Rest, change of exercise type to non-foot-stressing/non-wt-bearing & self-physical-therapy is probably all that's needed.