I'm not dispensing medical advice here, and I don't want anyone to view this comment as an excuse to "sit and wait" if they think they are having a health problem. That said, I am a repetitive quiter - it's really lame I know, but far too common. I'll quit for a month, sometimes 2, but invariably I end up feeling "over" my addicition, smoking one and having the self control to wait a week before I smoke another, and then I've proved to myself that I can, in fact, just have one.... I'm sure you've all been there.
Point being, I have experienced the effects of quiting many times, and I have felt heavy-chested almost every time. I don't know if it's related, but one way I try to inspire myself is by timing a 5k periodically (no I won't post my time, it sucks even when I'm not smoking,) and noting the improvement. During the first 3 or 4 days off the smokes, it's actually worse. I have a really hard time controlling my breathing during this period. Then, finally it gets better, and keeps getting better.
This is one possibility. For those of you who have been smoking a while and getting this, check your pulse. If it's high while this is going on, maybe you should cut back the niccotine. FYI - I've been talking with vendors in China the past few days about e-liquid, and some of them don't even want to sell 24mg.
My suggestion is put your liquid in a syringe and vape as you regularly would, always filling from the syringe. See how many mls you used. Multiply this number by the mg strength of your liquid. If the resulting number is higher than you were smoking and you weren't having these problems with cigs, get a lower strength liquid.
Some food for thought when you're figuring out how much is too much - the highest dose patch is 21mg.