It's not clover. The correct name is oxalis.

That is one of the Oxalis (Wood sorrel) species and it seeds very prolifically. Many times people will think that plants of this they have pulled out have returned when they have new plants growing from seeds. If, within 5 miles, you have any of these plants growing you will have them in your garden.

Since you are using weed killers, try Ortho weed b gon chickweed clover and oxalis killer. It may only be available in a concentrate so you will have to use your own sprayer and mix it with water.

Keeping in mind that Ontario has banned most uses of the common "weed" killers because of environmental concerns and that there are known adverse health affects to humans from most of them, and that simply pulling unwanted plant growth is the simplest and most environmentally friendly method of unwanted plant growth control, why spend money on materials that adversly affect your health as well as the health of the planet you live on?

I found this to be very clear and useful, but bear in mind that the campaign is more one of controlled co-existence. https://edis.ifas.ufl.edu/pdffiles/EP/EP51400.pdf