Crop rotation would help immensely. This spring, try planting each of your vegetables in a different spot from the place they occupied last year. This makes it harder for any pests to increase in numbers to the point they cause major trouble because they'll have to go looking for food. Even a small change would help.
It would also be useful if you got one or two bags of organic compost to use as top dressing along the bed. If you want to try growing pumpkins again, a bag of manure would also be useful to dig into their designated spot. Pumpkins need very rich soil. But even with rich soil, you just don't have enough room in your long, narrow garden bed to grow big pumpkins for Halloween carving. There are compact varieties of pumpkins, squash and zucchini, though, that don't need nearly as much space.
Names of these bush vine varieties include "snack Jack," which produces bowling-ball size pumpkins; "table king bush acorn," which produces small winter squash; and "black beauty zucchini."
About your carrots: I wonder how easy it is to cultivate the soil deeply in your retaining wall bed. It's important to grow carrots in loose soil where it's easy for their roots to penetrate. They hate clay.
You'd possibly be more successful with the "Danvers" heirloom carrot. This has short stubby roots that tolerate difficult situations well.
I should mention that if there are stones or rocks in your soil, carrots often develop forked, misshapen roots that sometimes are quite hairy. Another hazard is the carrot rust fly. The carrot variety "flyaway" and also "resistafly" are less attractive to this fly than other carrots.
Some crops take up very little space if you grow them vertically, and the soil at their feet can be used for other plants such as green onions or parsley. Cucumbers do very well climbing a small trellis.
It's also possible to grow pole beans up an obelisk.
I'm sure one reason your tomatoes grew so well is because concrete blocks are a heat sink - absorbing warmth from the summer sun in the daytime and slowly releasing it at night. If you like very hot peppers such as jalapeños and cayenne, you might be interested to know that these are even easier to grow than sweet peppers and produce masses of fruit.
Before you get warm enough weather to set out tomatoes, you could try growing some cold-tolerant fastgrowing salad crops in that place - arugula or radishes perhaps.
Try to keep a very close watch on the mint. It's incredibly invasive. If it gets its roots between those big concrete retaining blocks, it will be very hard to control its spread. Transplanting the mint into a separate container might save you a lot of grief in the future.
. Anne Marrison is happy to answer garden questions. Send them to her via email@example.com.