As you sorta said, stick to one at a time (I'd say no more than 2 simultaneously) and see about the P requirements of your plant, regardless of the soil report. Oh, I'm no expert, butt I can tell you what got my plants to do better last year, when it was too late. I'm gonna stop recommending to others about it butt this is the 4th/5th Diary I've seen having this problem. Hope it gets better 4 U. eg
You may know this but try to keep the pollination really cool. Put a bucket of water in the freezer. A small little tent, a bucket of ice etc. just an idea. Good luck Ian