The tail light isn't working on one side. Break lights are! But now the two in the center won't come on either. What can I do ? And where do I find

Be careful that you have the right type of bulb in the socket some of them were supposed to be 2 elements inside of them and some of them are meant to have only one element typically to be sure a light socket that has more than two wires going into it will be a double element bulb. As long as the existing wiring has not been modified by somebody or is broken or shorted together then this is the only problem I I think you may be having