Regarding addiction and lacking purpose.

Based on the information you have provided, it looks like you have a very reduced hedonic drive, and to seek some reward, you have developed pornographic addiction, which only gives a momentary surge of dopamine in reward circuits of brain and then there is a void. To fill it up, one tends to redo the past action that gave them a sense of fulfilment, in your case watching porn does that. Thus, it’s just like addiction to any substance. Your impulse control circuit is malfunctioning, secondly you seem be suffering from depression with declining executive functioning and lethargy. Your brain controls other body functions and any defect in homeostasis affects body and brain equally. Given the reason of ill health, needs evaluation of what exactly you are suffering from. Any infection or any autoimmune condition, any hormonal disorder etc.

Consult your psychiatrist, impulse control medicines, antidepressants and stimulants will be really helpful in your case.

You may as well consider talking to a clinical psychologist along with your Routine psychiatric medication.