Help please guys! Pics of problem

Im round about 3 weeks in to flower and all of a sudden boom my plants look drooping and leaves are yellowing I don't believe it's over nuting... Any suggestions? @

First thing, Relax.
1. what is your growing medium
2. are you Ph-ing your water?
3. how often are you watering
also, are the leaves yellowing at the bottom of the canopy or at the top?