Its only 12 and I'm a pack a day menthol smoker.
There's no good "guide" for what's equivalent to what. 12mg may be too high for you. I was a two pack a day smoker of menthols but I'm vaping 6mg right now (in fact, it's probably lower, I'm mixing myself and starting with 6mg plain nic, I'd have to sit down and do the math for X amount of flavor mixed in Y size bottle and yada, yada). I vary mine depending on time of day and other things. I have 12 to 18 for the times I would normally really, really want a cig (first in the morning with coffee or after a meal, times like that) but my regular stuff is 6mg and lower. Especially at night. Moderate to high nic at night will keep me awake late.
First suggestion is can you go back to the vendor that you got your juice from and get the same one but with 0 nicotine? That way you could mix them and cut the nic in half.
People also have different reactions to PG and VG. You say you have 50/50 right? You could try small bottles of 100% PG and 100% VG. See if there's a difference. You may need to go one way or the other instead of being in the middle.
Also, try not to "inhale" at all. In smoking, the nicotine (and the other 4,000 chemicals) are absorbed in the lungs. We're all used to drawing the smoke deep to get the nic. In vaping, it's absorbed in the mouth (and nasal passages if you do the exhale through the nose, which I do, I get more flavor and nic that way).
So you don't really need to get the vapor that far "back". Just hold it in your mouth a bit. Do more like a pipe or cigar "puff" kind of thing.
Some folks like "throat hit". The nic hitting the back of the throat. I never cared for it. Even as a smoker. I preferred a "smooth" kind of smoke thing. Had to get used to a different kind of inhale and fiddle with my nic level to get the vape I liked. For a while, I didn't really do an "inhale" much at all. Just drew the vapor into my mouth, held a bit, blew it out. Didn't stay with that for very long but kind of had to at first. My habit was to suck the stuff into my lungs. And lungs don't seem to like water vapor. I'd try coughing a lung up.
Also, don't forget, smoking screws with your throat. And those of us who smoked menthols were "masking" throat issues. Menthol does a soothing thing that masks irritation the smoke is causing. Your throat may just be irritated from the smoking and need some time to recover now that the smoke is gone. You might have to do a "cigar puff" kinda thing a while, give your throat some time to calm down.