Please Help !!!

My friend, what you have here is a textbook calcium deficiency and it makes perfect sense at this stage of your grow. If you're not using any kind of nutrient supplement then all the available nutrients within your soil medium will have been consumed by the plant or washed out by waterings within the first 4 weeks of it's life. Now that these girls are entering flower they are exceptionally hungry for all nutrients at this stage and in dire need of supplementation. This specific issue you have is easily resolved with 1ml/L of a calmag supplement such as Calmag+ by Botanicare or Calimagic by GHE. They're the most popular and commonly available on amazon. Either one will clear this up for you in short order and you need to maintain it on every/every other feed for the duration of the grow. To your other grow question which I'll also be putting up in short order - same goes. You need to start supplementing your plants with a base flowering nutrient immediately otherwise, they will continue to look worse and worse. I'd recommend a broad spectrum flowering nute such as Flora-bloom or Pure Blend Pro Bloom. You could use a commonly available tomato nutrient at this point if you had to. Essentially any kind of nutrient supplement with an N-P-K range that spans from low to high eg. 2-3-4, 3-5-8 for a fruiting cycle. Start feeding immediately and on every watering until you see improvement. Without this, your medium is now devoid of any and all nutrition that the plant needs to continue growing and it will eventually die without it. Hope it helps and good luck with it dude.👍