Jusblaz, If the yellowing started at the onset of flowering. Your P was way to high in veg to start. Always remember that when the leaves yellow out. They do not photosynthesize much if at all ! That means that your plant is less capable of feeding it's self as well as it should. That makes stress to the plant. Stressed plants are more likely to attract pests and contract molds and fungus problems. Green healthy leaves mean strong healthy plants and I would go as far as saying that, "If your plants had healthy green leaves all the way to the end (they do have a natural yellowing and die off, but no where near what you had !). You would have seen even more yield in size and weight!
If I may ask, what have you been feeding with?
What is the NPK of the feed for veg. and for bloom?
The "look" of low N is the most common guess in your situation. No amount of added N will help that problem!
Many read that added P in flower is needed by the plant. That is only somewhat correct! While added P in flower can and will add bulk to buds. The amount needed to add is about dbl that of veg stage, BUT more importantly is WHEN you up the P (this is usually accomplished by simply switching to bloom feeds).
SOME (not many) nutrient makers are quite right in their feed charts. Others are not so much and others still make wild and toxic (to your plant) claims about how to use their "line" of nutrients and "supplements".
A good rule of thumb when using synthetic nutrition is to continue the "veg" nutrient until week 3 or 4 (somewhat strain dependent). At that point you begin "bloom" food (some real quality nute makers actually up the N P and K in their nutrient mix in ratio's that are more "correct" and you DO start it as directed,,,,,,HESI and CANNA come to mind).
Then come the P&K boosters. These can be the problem as many novice growers can stumble at the idea of "More is better". It is NOT! Even with Hesi and Canna, I do NOT advise to follow their charts for boosters! I would use their boosters like this. At the start of week 4, Add the PK booster on day 1 and then skip to week 5. Use it on day one and day 4. Skip to the start of week 6 and add at day one and again at day 4 and again at day 7. Now drop all booster use and run to finish ( I almost always run at least a week longer then the breeders reports say to. Example; 8 week flower is usually 9-10 weeks).
Use of high P&K boosters in the range of 0-52-36 are simply way to high in P, PERIOD! Avoid these until you have plenty of grows under your belt and understand the problems they can create VERY fast, and how to avoid the problems with very discreet use (I still don't use these very often at all, if ever !).
The use of a good Silica in veg and to week 4 in bloom will help control the P use/uptake by the plant.
I like to use my own home made "Sweet Raw" for trich and terp increase! It does work!
If interested in that, ask about it. I've run out of time and need to go.
Doc