could be wrong, but it looks like a magnesium deficiancy. some would say sulfer. sulpher? but those 2 some together in magnesium sulfide. its been a while since ive had that problem, but i too am 2 weeks into flower. and that normally happens around that time. the plant is needing more blossom nutes. I would feed them some 0-0-7 or 0-0-3. beastie blooms is like 0-50-30, but i dont feed it that till late in the flower cycle.weeks 8-9-10.