Problem with using analogWrite() in arduino

Question

I am using Arduino Mega, Dc Motor and Cytron 10A motor driver. I want to control the speed of the DC motor. I am using HC-05 to control the robot. Here is my code:

Arduino:
#define AN1 12
#define AN2 9
#define IN1 13
#define IN2 11
char inChar;
void setup() {
  // put your setup code here, to run once:
Serial.begin(115200);
pinMode(AN1,OUTPUT);
pinMode(AN2,OUTPUT);
pinMode(IN1,OUTPUT);
pinMode(IN2,OUTPUT);
}

void loop() {

  if (Serial.available() > 0)
  {
  inChar = Serial.read();
  Serial.println(inChar);
  }


if (inChar =='F')
{
  analogWrite(AN1,100);
//  analogWrite(AN2,100);
  digitalWrite(IN1,HIGH);
  digitalWrite(IN2,HIGH);
}
if (inChar =='S')
{
  analogWrite(AN1,0);
  analogWrite(AN2,0);
  digitalWrite(IN1,HIGH);
  digitalWrite(IN2,HIGH);
}
}

Each motor is able to control speed when connected individually or commenting either analogWrite(AN1,100) or analogWrite(AN2,100). When both are present in code, code doesn't work. Is the problem due to higher baud rate?

However, my code works perfectly on using digitalWrite instead of analogWrite. Any help would be appreciated.