Ok, now would be a good time to show a diagram of how you have the serial interface hooked up. Are you using SPI as in MOSI/MISO? That's the SPI protocol. Or are you using the TX/RX pins? Because that's Serial. And you CANNOT be using serial with print to the Serial monitor AND communicating with the device.
And that, my friend, is possibly why you had a hard time earlier, before you deleted the Serial.print commands. You get erroneous data to both the usb serial interface and the sensor and vise versa.
You can define multiple Serial objects, only if you have multiple serial ports or serial multiplexing. If you are using SPI, you can have virtually as many devices as you have RAM for and different addresses for each one.
On serial, each device MUST be connected to their own TX, RX, pins and must have a common ground.
On SPI, each device is connected in parallel to all other devices, with a common ground.
On another note, this is why it's important to give us all the information. As @SteveMann said:
Welcome to the forums. You will find a lot of regulars here who just want to help. In the future, please don't call a Fritzing Lego picture a "schematic". As your projects get more complex, the Fritzing pictures are less useful to useless.
In order for us to really be effective, have resolved this last night, it would have been useful to have all pertinent info on hand.
Anywho, hope that clears some of it up for you.
If you still need help after this, we will need those schematics