Seems weird that you go from no buzz, to straight sick if the dose is only a few mgs apart, maybe it's just that you haven't found a strain that your body reacts well to. With my prescribed ADHD meds, which are amphetamines and dexotroamphetamines (powerful psychoactives, way stronger and dangerous compared to weed), there is a difference of about 10mg where my tolerance is in the perfect zone for no side effects, before full side effects (and that's with the brand I tolerate).

I had to go through 5 different ADHD meds to get the perfect one my body didn't reject and then I went through 3 dosage adjustments of the last med to finally get the perfect prescription that wouldn't make me sick (ADHD meds make you sick differently, it's mostly nausea, headaches and gastro issues that can be quite severe). It seems to me like you haven't found the perfect "prescription" of weed for yourself. Not that you even have to try to if you don't need weed for medical reasons anyway, but that's just what it seems like to me.

Psychoactive drugs tend to be hard to prescribe to people that have low tolerances (such as myself). I was able to find my perfect weed dosage and strain before I was able to find the proper ADHD ones (since I had to go see the doc repeatedly for ADHD drugs over the course of 4 years of testing, whereas weed was recreational already, so all I had to do was order some and test over a few months myself, no doctor visit needed).

Hopefully you get a good dosage if you're trying to find it for medical reasons.