You truly need to see a psychiatrist, as it sounds like anxiety and/or depression, but only a professional can tell you this. A GP is not qualified to properly diagnose you nor are they very familiar with the medications. You may need therapy along with medication, but your psychiatrist will know what route is best for you. You shouldn't have to live like this when there is so much help available for you. You always want to deal with a specialist since they are best trained in a particular area. Please don't waste another moment on this, get in with a psychiatrist and start getting your life back. We've all have been or are where you are right now, so know you're not alone and you will find lots of support here. Take care.....
Seconded. If one doctor isn't doing you any good, it's time to see another.
Good luck :).
The dosage on the melatonin may be the problem. With melatonin, less is more. 1mg is a good starting dosage; .5mg might even be enough. 5mg is too high, and 50mg is too high to be effective. My personal advice is to start with a therapist, not a psychiatrist -- you sound like you have a good doctor who is trying to help you without putting you on strong, perhaps unnecessary medication before finding out if something simpler will work. First, do no harm, remember, guys? If the simple things don't work, you can always get into the medication later -- it isn't going anywhere. But since medication only treats symptoms and doesn't cure, your doctor is seeking a cure -- if sleeplessness is really your problem it's a lot easier to fix than what psychiatrists deal in. You might also look into meditation and acupuncture for your back and your sleep.
Do you regularly consume Alcohol?
That could lead to a lot of those symptoms as well (especially if you have a night cap to help you fall asleep, it can often lead to waking up part way through the night, which in turn leads to anxiety/stress/irritability). Just thinking out loud here; not accusing or insinuating.