"Tight chest, breathlessness and lung pains" all warrant a medical check each on their own.
I suppose you're one of us nicotine addicts so have you tried pausing vaping and switching to patches or gum for a few days or a week just to see if those symptoms would ease?
Tasting juice in your mouth shouldn't happen, except with poor gurgling and spitting equipment. Getting nicotine liquid, especially high nic (you didn't say what strength you were using)in your mouth where it is absorbed very quickly and effectively can give heart palpitations to anyone. Try keeping a glass of water always at hand for rehydration and rinsing and spitting if necessary.
I'd suggest stopping or noticeably reducing your nicotine comsumption immediately and booking a medical check. Those symptoms could be caused by various things and you'd be better off finding out by what.
Less nicotine (e.g. switching to lower "mg" juice) could alleviate the symptoms, but you could also be sensitive to PG, VG or whatever flavouring or additives were in the liquid. Consider switching to a different well-known liquid brand you can get from a reliable source and while you're at it, consider getting a new good quality atomizer, battery and coils to rule out equipment as a contributor to your health issues.
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