Tender Breast

I would use some hot compresses on the tender breast. You just wet a washcloth or hand towel in water as hot as you can stand, then drape it around your breast until it cools. I used to do this right over the sink, just soak, wring out the washcloth, and drape for a few minutes, and repeat. It could be the start of a plugged duct and this will help open it back up.
Of course, if home remedies do not work, call the nurse or doctor tomorrow morning.

Good suggestions below, but I would also suggest just waiting a day before doing much beyond a warm compress. I would get tender after being engorged, and I think it was just from the tissue getting stretched out with all that milk. After 24 hours of normal pumping/feeding, the tenderness would be gone.

If you feel any hard spots (suggesting plugged ducts), or if you see red streaks or you start to run a fever (suggesting mastitits), then for sure take more action.

You could have mastitis, I used to get it every time I was in a situation like yours. If the warm compress and shower and nursing don't help within 24 hours call the obgyne. Mastitis needs antibiotics. Does your breast feel warm to the touch?

Teenmom is correct. I sometimes, used to take a really warm shower to help relieve the pressure and work on any plugged duct.