Short answer
Wilting normally means thirst, but a plant with damaged roots cannot take up water either, so it wilts in soil that is still wet. Check whether the soil is wet or dry first. Wet soil plus wilting points at the roots, most often drainage. Dry soil that runs straight through points at a root bound pot.
Listed in the order they are worth ruling out. It is normal for more than one of these to be happening at once, so work down the list rather than stopping at the first match.
The pot has no drainage hole and the plant wilts while the soil is still wet. Wilting normally reads as thirst, but a damaged root system cannot take up water either, so the same plant wilts in soaking soil.
What to check first
Slide the plant out of the pot and look at the roots. Healthy roots are firm and pale. Rotting roots are brown, soft, and smell sour.
The pot itself drains, but it sits in a saucer or a decorative outer container that holds everything draining through. The roots end up standing in that water, which produces the same outcome as having no hole at all.
What to check first
Lift the pot out of its saucer or outer container and look. If there is water in the bottom, it has been sitting against the roots since you last watered.
You said it is still in the pot it came home in, or that roots are showing at the drainage hole. A root ball that has filled its container holds very little water, so the plant runs out between waterings and wilts on a schedule that looks random.
What to check first
Look at the drainage hole for roots coming out of it, then slide the plant out and look for roots circling the outside of the root ball in a dense mat.
You said this was planted or bought in the last couple of weeks. Until its roots grow out past the original root ball, the plant can only drink from that small volume, so watering the ground around it does not reach anything.
What to check first
Push a finger into the soil at the base of the plant, inside the original root ball rather than out in the surrounding bed. That is the only place its roots can reach yet.
Mentioned because it is common in summer and quick to rule out yourself. Dark containers absorb more heat than light ones, which dries the mix faster and raises the temperature around the roots.
What to check first
Put your hand flat against the sunny side of the pot in the middle of the afternoon. If it is hot to the touch, the root zone is hotter than the air around it.
Still not sure
This is exactly what your county Extension office answers, for free. They are the local horticulture experts for your area, they know what is going around this season where you live, and they will look at a photo.
Find your local Extension officePollinator Patch gives you watering and seasonal care for the plants you already own, written for your region rather than for gardening in general.