I changed a light switch in a 2 and floor bedroom. Now my kitchen lights don't work. All the outlets work fine just no light.

Somehow you missed a wire or disconnected one. Check for a loose pigtail or back stabbed wire. What were the wire colors at the switch?

Somehow you missed a wire or disconnected one. Check for a loose pigtail or back stabbed wire. What were the wire colors at the switch?

3 black 2 tied together 1 separate.

How were the blacks that were tied together connected to the switch? Are you sure there isn't a small pigtail somewhere. No whites? I would surmise the 2 tied together are hot and the separate one goes to the other side of the switch but without a white passing through I'm not sure. Are any of the wires recolored from white?

Did you separate all the blacks at the switch and then reconnect them? If you you did not put them back together the same way.