It's very hard to OD on codiene as your liver enzymes max out before you can convert it all to morphine (usually*). However if the tablets contain another drug such as paracetamol (acetaminophen) you can permenantly damage your liver with these instead. Be careful about how much of these you take as your weight won't help with this.
Read the packet and just don't take more than it says, especially considering your body will be under enough stress as it is already.
Here are the side effects of T4
CODEINE/ACETAMINOPHEN - ORAL (Tylenol with Codeine) side effects, medical uses, and drug interactions.
Also you will feel really ill (really sick can't stress this enough) if you take too much codeine.
Have you considered meditation you could use it to disasociate from the pain.
*covering myself here, i'm not a doctor this is theory