You might have a ground-nesting species of Yellowjacket wasp in the area if you are being stung without having knowingly provoked anything. It's true that solitary ground-nesting bees and wasps, which comprise the majority of our bee/wasp species diversity, are not inclined to sting, especially repeatedly or as a group. Females of those solitary bee and wasp species nest singly, even if they form a grouping of several nests near each other due to appealing habitat, so each female would only be defending herself if she were to sting, which they generally avoid doing. (Plus, the venom of many of those species is not intended for mammals the way social wasps defending a shared nest use their stings, so it's also often less likely to be as impactful to us even when they are capable of stinging.)

Yellowjackets have a reputation for being easy to agitate and quite defensive around their nests, more likely to sting than just about any other wasp or bee, including for what appears to be no apparent reason. (Certain odors might trick them into stinging if they happen to mimic alarm pheromones that stinging wasps leave behind for their nestmates to find and attack.) Since some species of Yellowjacket nest in the ground (as opposed to in a hanging nest or wall void), these are our prime suspects for this situation. If found and confirmed to be Yellowjackets, and if you need to eliminate the nest instead of being able to avoid it until frosts in autumn (when the workers will all die and the problem will resolve itself), you can carefully use a wasp spray to kill them. Follow all label directions carefully to both have the pesticide be as effective as possible while maintaining low personal risk from use of the insecticide. Nests are not re-used from year to year. Wasps of all types are beneficial in landscapes because they prey on insects we consider pests, but we realize not all of those apt to sting can be tolerated near homes.

Miri