They don't have to paint the entire picture on the affidavit to file the charges, only give enough information to establish the probable cause for the charges to be filed. Your preliminary arraignment/Preliminary hearing is where they actually bring out the real testimony about what happens and you have the ability to crossexamine or bring up your own witnessses.

What are you charged with?

I suspect you didn't have a lawyer at the prelim.

If this was a summary offense, your plea at the prelim (I suspect you also waived everything and was tried by the magistrate) stands.

If this is a misdemeanor, then even if you negotiated a plea, it doesn't mean anything yet. Even if you waived the prelim, you still have to go up in front of the common pleas judge for an arraignment and then a "trial" (really you'll just admit the charge and be found guilty) and sentencing. Most likely a PSI will be conducted in the interim.

If the latter is the case (and you haven't been to trial), then you MUST find get a lawyer NOW!