I was at 48mg+ when I first started but I also smoked 1 - 2 or more packs a day and I smoked cloves which are more like a cigar than a cigarette....but once my nic fits stopped I was able to drop down to 24mg and then slowly drop my nic until now I'm down to 1.5mg
no not really shortness of breath, well aside from being an ex-heavy smoker with asthma and bad allergies

but there is an adjustment period from smoking to vaping and if you remember when you first started smoking it didn't feel too good on the lungs either but yet you kept on smoking

plus your body is finally starting to get rid of all that tar and other buildup in your lungs
however as I've mentioned (a few times) in your other thread, if it is really concerning you, you really should speak to a doctor and you do not at all have to tell them you are vaping.
I do not like a throat hit so I use max vg
another thing that you could try is to not inhale the vape...just hold it in your mouth and then exhale...with vaping, unlike smoking, you don't need to inhale it into your lungs, the nicotine can be absorbed in your mouth. When I first started vaping I could not inhale it, later I found out that's because I have issues with pg so yeah....that and my lungs were healing from all the abuse they took and collapsing and all that fun stuff....
so you could try that instead of inhaling the vape into your lungs, just hold it in your mouth for a bit then exhale until your lungs have had a chance to heal....but again, you really should talk to a doctor because there could be something else going on (ie something viral, or adult onset asthma, etc, something that only the doctor would be able to determine or rule out)