There's no legal limit on how much you can drink with a child in the house. It's not about 'going over the limit'.
It's about whether the state you are in makes you incapable of looking after a child and therefore puts the child at risk.
If someone has a very low alcohol tolerance, or is drinking on top of medication, or has other medical conditions that mean alcohol affects them severely, they might be incapable after one glass of wine. For almost a year when I was younger, I was on medication which meant that I pretty much couldn't function properly if I had a drink - it felt like I was about to slip into unconsciousness, like the moments before you fall asleep under a general anaesthetic. I wouldn't have been safe to care for children in that state. But under normal circumstances, I could drink a bottle and a half of wine and still be capable of looking after a child (not that I'd want to - but I'd certainly be awake, capable of putting a child to bed safely, reading them a story etc and easily woken up if they needed me in the night).
I find it quite concerning that a) you think you just 'appear' intoxicated when you mix booze with meds, rather than actually being intoxicated and b) there were sufficient concerns for police and a social worker to remove a child from your home in the middle of the night. I also find it concerning that you're just talking about getting repeated calls from 'duty safeguarding' as if that's just a normal thing that happens, and that you don't seem to really grasp what this means or what the concern is. Your passivity over this seems really odd to me.
I think that if you are mixing alcohol with medication in a way that makes you 'appear' intoxicated 'because you need to relax' while you are looking after not only your own child but also someone else's child, that's not a great sign, to be completely honest. I'm sure it's perfectly possible that the reports of you being drunk are indeed malicious, but on the other hand it's also perfectly possible that you're not being at all honest with us (or more likely with yourself) about the full picture.