Vaping is so much more complex than smoking - I don't think that is stated enough. It can be terribly frustrating when you see it working for so many people yet it's not working for you, not to mention the cost of trying to find what works. But you found your way here and that is hopefully the first big step to identifying and fixing your issues at minimal further cost to you.
I'm an IT guy so not normally thrown off by such things, but even I have been muddled by all the technology, terminology and conflicting advice attached to vaping. Until recently I was caught up in the hype (You Tube etc) and was convinced I needed to "sub-ohm" and vape "straight to lung (STL)". No! I was a heavy smoker and I just needed a setup that would replace that addiction and provide the easiest transition from smoking to vaping. The fancy stuff can come later (if and when I want it).
But here's the thing. Equipment and juice issues aside (I'll let the experts here help you with that), I discovered the simplest thing recently that has made a massive difference to my vaping experience and that is "how" I was actually vaping. I was using too high watts and I was sucking way (way) too hard. I hadn't realised this before as the equipment I was using was masking this problem. I have now reduced my watts down to the 9-11 range and I take much longer and very gentle draws into the mouth before quickly inhaling and exhaling. The result is no more coughing, no light head, and a much more mellow yet flavoursome vape. I smoked out of pure need before, but I actually look forward to my next vape now. It's so enjoyable compared to smoking.
Until you find a vendor you can trust (the ones on here are great BTW from my experience so far), just listen to the experts advice on here and I am sure they will get you sorted ASAP. Also, you mentioned in your other thread that your Mrs was vaping without issue. Has she tried your equipment and juice just to see if it seems right to her or have you tried hers? Just a thought.
Good luck - I really hope you stick with it and the guys here will sort you out I'm sure.