Without more details I can only take a few guesses. Please take a look at online pictures of pigweed, white snakeroot, Galinsoga, Galeopsis (hempnettle). Compare to what you have.
If none of the above match, you can let one plant grow, flower and take a picture that clearly shows how many flower petals and what shape the petals are. Include the time of spring or summer that it flowered, and the size and color of the flower. You can let the flower develop a seed pod and send us a picture of that, too.
I may be able to ID it if you can give me these details: is the stem square or round, is the sap in the stem clear or milky, are there prickles or noticeable hairs on the stem or leaf, size of the leaf ( length and width), size of the plant, is it found only in your pots, or is it growing elsewhere, is there any scent noticeable when leaves or stems are rubbed or crushed - like mint, onion- try to describe its smell; pull a plant up and describe the roots- are they fine and multi branched or are they thick and carrot-like, do the roots have a scent or a color?
As you can see we need to consider many things. One note- if you decide to rub, crush or break a stem to answer these questions- please where gloves. Some people have a skin sensitivity to some plants.
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