Is your problem that you get an error when you read your sensor or that you don't get anything?
If it is an error, I agree with
@Knikki to contact Abbot.
If you get nothing it may be that you have not correctly positioned the reader.
I find my Libre is very sensitive to the position of the reader be it the official Libre Reader or my phone. I think the NFC is very directional so the reader has to be directly over the sensor.
With my phone, I have learnt where the NFC reader is (near the camera). So, I put my finger over the camera and touch the sensor with the back of my finger and it works every time.
As for pain - no no no. That doesn't sound good.
If you mean you can feel it sometimes (probably when you move your arm in a certain way), that is not unusual.