Is it okay to use both the backwire holes and the side terminals on an electrical outlet?
There is no problem connecting wires to both the "back stab", and screw terminals of a receptacle.  As long as the terminals are rated for the size of wire being attached. For example. Most "back stab" terminals are rated for 14 AWG solid copper wire, whereas screw terminals are usually 12 or 14 AWG solid or stranded copper. 

With that said... It sounds like your receptacles might be hooked up backwards.  The black ungrounded "hot" conductor should be connected to the brass colored screw, which is on the side of the receptacle with the shorter slot (at least in the US).