SoftwareSerial mySerial(4,A2); // RX, TX
Do you really have a mySerial connected to those pins? I find that hard to believe. Use an instance name that makes sense with respect to what you REALLY have connected to those pins.
I am unable to use pin 0 and 1.
Why? Is it because you need them to talk to the PC?
My only option is to use two software serials, one for SIM900 and one for RFID.
And that isn't an option since you really need both instances listening at the same time, don't you. You need a Mega.