When can I start my fall garden 🪴?

I've about given up on gardening. I only planted two tomato plants, green onions and a couple of zucchini. The green onions did well and are gone. The tomato plants aren't growing, but I have several green tomatoes on them. The zucchini keep putting on fruit that grows to about four inches, then shrivel and fall off. That could either be lack of pollination or inconsistent water. The weather definitely hasn't co-operated again this year. It was cool, no sunshine for most of the month of May with huge amounts of rain. Finally getting some sunshine, but now it's going to be HOT. Can't win.