your not in the ideal range of pH for your soil, try and get that down to 6.5 - 6.8. your also in the 3rd week of flower so your plants NEED nutes, i think your nutes are not enough, but you can test for that, there are some test kits out there to find out what your nutes are in your medium. One other thing, i was looking at your pics, do you have more than one plant in per pot or are they "topped". I'm wondering if you are short on the pot and you might also be root bound. This will result in your plants not getting the water and nutes they need.