OK, the thing here is your expecting too much too soon.
Buds form and grow to a "running" size till (strain dependent) about week 6.....At that point is when the "BULKING" phase begins and you will see over the next few weeks till finish that the buds will REALLY build up size and weight. The more and fastest growth comes the closer to harvest.
This is where the "extra" P&K actually DO the work many nutrient makers say their high P&K amounts do from the flip, which, for the most part, is simply hype! This extra high P&K shit used by them tends to make your plant yellow out to soon and cause lost size and yield!
You don't say what you use or how much/how often. I'll say this. The way your plants look, you haven't really overused the given P&K to levels of tox. Nicely done!
Be patient!
P.S.
Defoliation, the way it looks you did it = makes for smaller buds!