Bug in code of Self-Balancing Bot

Question

1)The values drifts to the extreme every time I run this , I guess this is due to my mistake in the calculation of angles or in the filter that I have applied which I have been trying to but can't find it. 2)I have tried to calibrate MPU many times but failed as the x-axis value is showing 0 only when I tilt the bot to 12-14 degrees on x-axis(data from only accelometer),(if you can just tell me the variable to modify)

#include <Wire.h>
long accelX, accelY, accelZ;
float gForceX, gForceY, gForceZ,elapsedTime;
long gyroX, gyroY, gyroZ;
float rotX, rotY, rotZ;
double x,y,z,dx,dy,dz,ex,ey,ez,desx=0,desy=0,desz=0;
float PID, PWM, error, previous_error,timePrev,time1;
float pid_p;
float pid_i;
float pid_d;
float rad_to_deg = 180/3.141592654;
/////////////////PID CONSTANTS/////////////////
double kp=2;
double ki=0;
double kd=0;
int motor1pin1 = 2;
int motor1pin2 = 3;
int led = 9;           // the PWM pin the LED is attached to
int brightness = 0;    // how bright the LED is
int fadeAmount = 5;
void setup() 
{
  Serial.begin(115200);
  Wire.begin();
  pinMode(motor1pin1, OUTPUT);
  pinMode(motor1pin2, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(13, OUTPUT);
  setupMPU();
  delay(500);
}
void loop() 
{
    timePrev = time1;  // the previous time is stored before the actual time read
    time1 = millis();  // actual time read/
    elapsedTime = (time1 - timePrev) / 1000; 
    recordAccelRegisters();
    recordGyroRegisters();
   processangle();
    Apply_PID();
    printData();
    delay(100);
}
void right(int PWM)
{
   analogWrite(9, PWM);
  digitalWrite(motor1pin1, HIGH);
  digitalWrite(motor1pin2, LOW);
  digitalWrite(13, HIGH);
  Serial.println("RIGHT");
}
void left(int PWM)
{
   analogWrite(9, PWM);
  digitalWrite(motor1pin1, LOW);
  digitalWrite(motor1pin2, HIGH);
   Serial.println("LEFT");
}
void stopper()
{
   analogWrite(9, PWM);
  digitalWrite(motor1pin1, LOW);
  digitalWrite(motor1pin2, HIGH);
   Serial.println("STOPPED");
  }
void setupMPU()
{
  Wire.beginTransmission(0b1101000); //This is the I2C address of the MPU (b1101000/b1101001 for AC0 low/high datasheet sec. 9.2)
  Wire.write(0x6B); //Accessing the register 6B - Power Management (Sec. 4.28)
  Wire.write(0b00000000); //Setting SLEEP register to 0. (Required; see Note on p. 9)
  Wire.endTransmission();

  Wire.beginTransmission(0b1101000); //I2C address of the MPU
  Wire.write(0x1B); //Accessing the register 1B - Gyroscope Configuration (Sec. 4.4) 
  Wire.write(0x00000000); //Setting the gyro to full scale +/- 250deg./s 
  Wire.endTransmission(); 
  Wire.beginTransmission(0b1101000); //I2C address of the MPU
  Wire.write(0x1C); //Accessing the register 1C - Acccelerometer Configuration (Sec. 4.5) 
  Wire.write(0b00000000); //Setting the accel to +/- 2g
  Wire.endTransmission(); 
}
void recordAccelRegisters() 
{
  Wire.beginTransmission(0b1101000); //I2C address of the MPU
  Wire.write(0x3B); //Starting register for Accel Readings
  Wire.endTransmission();
  Wire.requestFrom(0b1101000,6); //Request Accel Registers (3B - 40)
  while(Wire.available() < 6);
  accelX = Wire.read()<<8|Wire.read(); //Store first two bytes into accelX
  accelY = Wire.read()<<8|Wire.read(); //Store middle two bytes into accelY
  accelZ = Wire.read()<<8|Wire.read(); //Store last two bytes into accelZ
  processAccelData();
}
void processAccelData()
{
  gForceX = accelX / 16384.0;
  gForceY = accelY / 16384.0; 
  gForceZ = accelZ / 16384.0;
  x= (RAD_TO_DEG * (atan2(-gForceY, -gForceZ)+PI));
  y= RAD_TO_DEG * (atan2(-gForceX, -gForceZ)+PI);
  z= RAD_TO_DEG * (atan(sqrt(square(-gForceY) + square(-gForceX)) / -gForceZ));
 /* x=map(x,340,11,-90,90);*/
Serial.print(&quot; AccelX=&quot;);

Serial.print(x);
}
void recordGyroRegisters() 
{
  Wire.beginTransmission(0b1101000); //I2C address of the MPU
  Wire.write(0x43); //Starting register for Gyro Readings
  Wire.endTransmission();
  Wire.requestFrom(0b1101000,6); //Request Gyro Registers (43 - 48)
  while(Wire.available() < 6);
  gyroX = Wire.read()<<8|Wire.read(); //Store first two bytes into accelX
  gyroY = Wire.read()<<8|Wire.read(); //Store middle two bytes into accelY
  gyroZ = Wire.read()<<8|Wire.read(); //Store last two bytes into accelZ
  processGyroData();
}
void processGyroData() 
{
  rotX = (gyroX / 131.0);
  rotY = gyroY / 131.0; 
  rotZ = gyroZ / 131.0;
  Serial.print(" GyroX=");
  Serial.println(rotXelapsedTime);
}
void processangle()
{
  dx=0.98 (dx + rotXelapsedTime) + 0.02x;
  dy=0.98 (dy + rotYelapsedTime) + 0.02y;
  dz=0.98 (dz + rotZelapsedTime) + 0.02z;
  ex=dx-desx;
  ey=dy-desy;
  ez=dz-desz;
  Serial.print("After Filter Angle");
  Serial.println(ex);
}
void Apply_PID()
{ 
  float l=(float)ex;
  pid_p=kpl;
  pid_i = pid_i+(kil);

pid_d = kd ((l - previous_error)/elapsedTime);
PID = pid_p + pid_i + pid_d;
/Serial.print("I=");
Serial.println(pid_d);
Serial.print("p=");
Serial.println(pid_p);*/
Serial.print("PID");
Serial.println(PID);
if(l>5.5 || l<5.5)
  {
    if(l<0)
    right(PID);
    else
    left(PID);
  }
  else
  {
    stopper();
    }
previous_error = l;
}
void printData() 
{
  /Serial.print("Gyro (deg)");
  Serial.print(" X=");
  Serial.print(rotX);
  Serial.print(" Y=");
  Serial.print(rotY);
  Serial.print(" Z=");
  Serial.print(rotZ);
  Serial.print(" Accel (g)");
  Serial.print(" X=");
  Serial.print(gForceX);
  Serial.print(" Y=");
  Serial.print(gForceY);
  Serial.print(" Z=");
  Serial.println(gForceZ);/
 /* Serial.print(" PWM");
  Serial.println(PID);*/
}