I am currently stuck in the hell (migraine, diarrhoea, sickness, runny nose/eyes, full body pain, no sleep, miserable) that is coming off the 30-500 co codamol after years of taking 8 a day. Taking them for migraines had contributed to the Hell. All taking codeine does for the migraine is turn down the pain, not treat the cause. Is yours prescribed for migraine?
If I get stuck in a state like you are it's normally due to one or more of the below:
An infection (always get a wicked headache);
Neck spasm, a good massage helps loads;
Have used too many painkillers as they are triggering the pain
If you can take NSAIDs (I can't) take some with paracetamol, full fat coke, triptans if prescribed and a large glass of water and lie still in a dark room with no screens.
Honestly, Google medication overuse headache
Good luck