HELP!! My plant is about to die, what do I do?!!

I don't like to be cornered into endorsing one fertilizer over another as there are hundreds on the market that will do the job and then some. As long as the ratios are correct for both vegetation and flower and applied in a responsible manner, good things will happen. The biggest problem that I see new growers make is abuse/overuse of fertilizers in soilless growing mediums. This causes a cascade of problems not the least of which is salt toxicity and resulting pH imbalance. In other words you can "burn" or damage a plants roots/vascular system with any nutrient if applied in a irresponsible manner. I have had success with both mineral-based and, "organic" fertilizers. Currently using "Earth Juice" products and "Advanced Nutrients" products in a side by side comparison on some SLH cuttings but the control groups are neither under laboratory conditons or large enough to produce useful data. The results might mean something to me as the plants are from one, single "mother" but are of little use unless the results can be duplicated over a wide range of plant material, including other cannabis phenotypes.

I don't think it's the nutrients. You typically don't even need them for at least the first month. Even at 3 weeks your girls looking a little small. Don't over water and get them under more light.