Serial.availabe() loop is working only for the first time - arduino

Question

I am working on RFID. I am sending data through serial monitor and the Serial.available is not identifying the data after the first time, its working perfectly fine only once after reopening the serial port.
I have tried all the possible changes I could do in the code. I want that when I run this code, then after entering the data in serial monitor it should show "Scan the mifare card" and after scanning the card it should perform read or write action.
#include <SPI.h> // include the SPI bus library
#include <MFRC522.h> // include the RFID reader library
#define SS_PIN 10 // slave select pin
#define RST_PIN 9 // reset pin
MFRC522 mfrc522(SS_PIN, RST_PIN); // instatiate a MFRC522 reader object.
MFRC522::MIFARE_Key key; // create a MIFARE_Key struct named 'key', which will hold the card information
void setup()
{
Serial.begin(9600); // Initialize serial communications with the PC
SPI.begin(); // Init SPI bus
mfrc522.PCD_Init();
// while (! Serial); // Wait untilSerial is ready - Leonardo
// Serial.println("Enter data");
}
String incomingStr;
byte blockcontent[16];
int count=0;
String arr2[6];
int arr3[6];
int u2=0;
String arr[16];
int arr1[16];
int u=0;
int y;
char action;
//int newc=0;
void loop()
{
// Serial.println("bahar");
if (Serial.available())
{
doReceive();
int newc=0;
while(newc==0)
{
if (!mfrc522.PICC_IsNewCardPresent())
{
if(count==0)
{
Serial.println("Scan your mifare card %");
count++;
}
}
else
{
newc=1;
}
}
if (!mfrc522.PICC_ReadCardSerial())
{
return;
}
if(action == '%')
{
doWrite();
}
else if(action == '$')
{
doRead();
}
else if(action == '^')
{
for(byte i = 0; i < mfrc522.uid.size; ++i) { // read id (in parts)
Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
Serial.print(mfrc522.uid.uidByte[i], HEX);
}
Serial.print("*");
}
mfrc522.PICC_HaltA();
mfrc522.PCD_StopCrypto1();
Serial.flush();
}
}
void doReceive()
{
incomingStr = Serial.readString();
int sto = incomingStr.indexOf(')');
action = incomingStr.charAt(sto+1);
y = sto+2;
for(int j = 0; j < sto; j++)
{
if(incomingStr.charAt(j)!= ' ')
{
// Serial.print(incomingStr.charAt(j));
// arr[u]=arr[u].concat(incomingStr.charAt(j));
arr2[u2]+=incomingStr.charAt(j);
}
else
{
// Serial.println(arr[u]);
u2++;
}
}
for(u2 = 0; u2 < 6; u2++)
{
arr3[u2] = arr2[u2].toInt();
key.keyByte[u2] = arr3[u2];
//Serial.println(key.keyByte[u2]);
}
}
void doWrite()
{
int block = 1;
for(int i = 0; i < incomingStr.length(); i = i+16)
{
if(block == 3 || block ==7 || block ==11 || block ==15 || block ==19 || block ==23 || block ==27 || block ==31 || block ==35 || block ==39 || block ==43 || block ==47 || block ==51 || block ==55 || block ==59 || block ==63)
{
block=block+1;
}
for(int u = 0; u < 16; u++)
{
blockcontent[u] = 0;
// Serial.println(arr1[u]);
}
String s1 = incomingStr.substring(y + i, y + 16 + i);
s1.getBytes((char *) blockcontent, 30);
writeBlock(block, blockcontent);
block = block + 1;
}
Serial.println("Data written successfully*");
}
void doRead()
{
int block = 1;
for(int i = 0; i < 4; i++)
{
if(block == 3 || block ==7 || block ==11 || block ==15 || block ==19 || block ==23 || block ==27 || block ==31 || block ==35 || block ==39 || block ==43 || block ==47 || block ==51 || block ==55 || block ==59 || block ==63)
{
block = block + 1;
}
byte readbackblock[18];
readBlock(block, readbackblock); // read the block back
//Serial.print("Block contains: ");
for (int j = 0 ; j < 16 ; j++) // print the block contents
{
Serial.write(readbackblock[j]);//Serial.write() transmits the ASCII numbers as human readable characters to serial monitor
}
//Serial.println();
block = block + 1;
}
Serial.println("*");
}