I am trying to add 3 pendant lights to the same switch as a light in the room. The power source runs to the light first, then to the switch. I tapped into the wire from the switch to the light. I connected whites to whites, blacks to blacks, and grounds to grounds. Now the pre-existing light fixture is constantly on and no power is running to the new pendant lighting. The switch does not control anything now. I would like to have the switch control all of the lights at once. Please help if you can.

Well, you did it wrong. There is no neutral at the switch when power comes into the fixture. Wire as below.

Thank you so much I will try to fix this in the morning.
Thank you

Does the wiring for the pendant lighting need to come directly from the light fixture or can I tap into the wire which goes from the fixture to the switch?

From the light fixture.

There is no neutral in the cable going to the switch. The white wire going to the switch is a hot. The white takes current to the switch and the black brings it back, when the switch is on. Your are suppose to put a piece of black tape on each end, (or paint black) of the white wire going to the switch, to signify that it is hot. It is not a nuetral.

Note the connection of the white (neutral) of the pendant to the white (neutral) of the existing light fixture.