if they are white bugs that look like ants, but I never knew that they would get into onions. This is a new one on me. Are they eating or burrowing in the onions? Or are they just all around the area where your onions are planted? If they are just swarming around that area, it could be that there is buried wood in your garden. If they are eating the onions, all I can say is WTF.

I can't answer any of your questions, but having more info might help someone who is more knowledgeable. I have seen cuke leaves turn yellow in two different situations...one was lack of water and the other seemed to be too much sun. But the plants continued to produce. Maybe there is a nutrient that it needs to both keep the leaves healthy and produce the nice cukes?

The cucumbers are getting the heck watered out of them via me and the rain. I also put fertilizer spikes in them and they are still producing like crazy.

I'm just sad about the onions .

We all have them. I know how sad it is, I have had more than my share of problems and failures. Live and learn and hope for great garden weather. After growing a small garden myself, I don't know how people make a living as farmers with all the things you have no control over. Good luck with it.