Thats the result of not feeding enough my friend . Seeing as your just starting flowering your plant needs a good PK boost . I say this because it will help facilitate the transition from VEG into FLOWER and also help facilitate the development of bud sites . What you are suffering from is a mix of the PK deficiency . I would boost the PK solution in your nutrient regime for the first week of flower then slowly decrease over time till its time to harvest . I may also suggest that you add additional CalMg to your mix because during the flower process the plant will suck that right up and if your not ontop of that you will run into CalMg problems along the way . I cal already see some CalMg problems starting as the yellowing in between the veins of the leaves indicates that clearly to me . I hope this information helps you to understand the slight problems you are dealing with and the very easy way to correct it to be back on track . Over all your plants look healthy just take your time and they will be rocking and rolling in no time . -Happy Growing!