Hi
@Leafmealone! This looks like a Potassium (K) deficiency to me. After 3 weeks of vegetative stage your plant is now going to enter pre-flowering stage, but there is not enough Potassium in your soil for its development. What kind of soil are you using (brand)? Do you check the pH of your waterings? If so, what pH range have you been playing with on this baby? Give her a good meal with the fertilizer of your choice, mix veg and bloom nutrients for the next 2 weeks, and she should be fine. Hope this will help, keep us up-to-date and happy growing 👊