GPS - Location sempre nulo

Estou tendo problema para obter uma localização valida,pois sempre volta nula mesmo com o gps ativo e outro app obtendo coordenadas corretamente.

Na minha Activity:

GPSTracker gps = new GPSTracker(this);

        if (!gps.isGPSEnabled) {
            Toast.makeText(this, "Favor ativar o GPS", Toast.LENGTH_SHORT).show();
        } else {
            Location l = gps.getLocation();
            if (l != null) {
                txtLat.setText(String.valueOf(l.getLatitude()));
                txtLon.setText(String.valueOf(l.getLongitude()));
            } else {
                Toast.makeText(this, "Localização nula!", Toast.LENGTH_SHORT).show();
            }
        }

Meu GPS Tracker é: GPSTracker extends Service implements LocationListener

Codigo do meu getLocation:

locationManager = (LocationManager) mContext
                    .getSystemService(LOCATION_SERVICE);

            // getting GPS status
            isGPSEnabled = locationManager
                    .isProviderEnabled(LocationManager.GPS_PROVIDER);

            // getting network status
            isNetworkEnabled = locationManager
                    .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

            if (!isGPSEnabled && !isNetworkEnabled) {
                // no network provider is enabled
            } else {
                this.canGetLocation = true;
                // First get location from Network Provider
                if (isNetworkEnabled) {
                    locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER,MIN_TIME_BW_UPDATES,MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("Network", "Network");
                    if (locationManager != null) {
                        location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }

                    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {

                    }
                    locationManager.requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("Network", "Network");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
                // if GPS Enabled get lat/long using GPS Services
                if (isGPSEnabled) {
                    if (location == null) {
                        locationManager.requestLocationUpdates(
                                LocationManager.GPS_PROVIDER,
                                MIN_TIME_BW_UPDATES,
                                MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                        Log.d("GPS Enabled", "GPS Enabled");
                        if (locationManager != null) {
                            location = locationManager
                                    .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                            if (location != null) {
                                latitude = location.getLatitude();
                                longitude = location.getLongitude();
                            }
                        }
                    }
                }
            }