Hi Leah, One easy way to see if its a pup problem or switch or grounding is as follows.
Set your volume level (Remember of course that the norm is for the bridge to be louder than the neck. Place the switch in the "Neck"only position and strum a chord then do the same in the "Bridge Only" position
If there is a significant difference here are some possible reason 1) the connection to the PU switch is bad...If dull looking joint re solder, it should be bright. 2) the ground from the bridge pu is bad re solder to top of volume pot. 3) the pu is short circuiting (New pu required)
Check also that there is a good connection on the switch between the common and bridge terminal.
Hope this is of assistance.
Fenderphil