You already know that ODs, whether they be with over-the-counter meds or prescription drugs, are highly unlikely to succeed. I'm sorry to say that you have significantly greater chances of ending up trapped in a psych ward than of obtaining your goal. It is important to also consider the potential for long-term physical impairment. Even if you don't intend to live in the long term, such impairment can massively worsen whatever quality of life you do have until then, and can also be an obstacle to future attempts, should that be something you decide for later on.
I'm sorry that you are at a point where you have nothing else available to you, and nothing else that you see you can do. I'm sorry that your body is a source of misery for you. But as someone who has attempted to OD on paracetamol, as well as on a prescription psych med, I with my own personal experience am compelled to tell you that it can only make things worse.
I know all too well that this isn't what you want to hear. But even when we feel we have hit rock bottom, we need to consider that it's possible there's a pickaxe nearby that can take us even lower than we thought possible. An OD is such a pickaxe. I don't wish suffering upon you further to what you already experience, so I would advise you not to take the OD of the sertraline and melatonin. I'm sorry this is not what you want to hear. I hope you can find a path to peace for yourself, in some way.
