No you are not pre -flower a good sing of pre-flower is the white hairs start to grow and in groups of more than just 2. Nitro def. you could have or it could be over watering. Let the soil dry up some and watch plant reaction. If the yellow fades its the water if not try sprinkling a layer 1/8 inch thick horse manure on top of your soil. The next time you water the nitro will be delivered to your roots greening up everything. Horse crap is a gentile way to help the plants. You should always pH your water to 7. This will allow your plants to consume what they need nute wise. If the tips of the leaves look burnt and not just weak you may have to much nitro. It is fixable by flushing your plants roots with pH 7 water. Your choice of nutes is not advisable. I suggest 50/50 soil mix horse manure / local soil for entire veg. No nutes needed until flower or at least 2 months. That will help eliminate allot of messing with the plants and allow for a more natural healthy grow. Over all for being from seed your plants look great.