Left taillight is out but brake light works

This could be a bad socket,remove bulb and check inside of bulb socket,socket may need replacing,if you are using correct bulb.

I checked the sockets i replaced with correct bulbs so confused on the problem because it only works when i press the brake but not signal or running light the right side works fine

Does the front blinker on that side work?

If not it may be in the blinker switch assembly is bad.

Yes flashes very fast but nothing on the rear taillight

It will be in the wiring to the left rear of van if front is flashing,do you have a trailer wiring harness on it,if so may be a good place to start your search.

I checked out the trailer harness and the harness that plugs into the tail light itself i have no idea i think there could be a ground problem i cant find a diagram to help me god so fustrated with this problem i dont know what to do