Well quitting smoking and starting a work out program at the same time is probably stressing your body a fair bit, it sounds like you are young and if you can quit cold turkey that's great. But you have said you tried several times before, therefore I'm not going to tell you not to vape, it's about harm reduction. If you can't make it cold turkey then absolutely go to vaping then gradually reduce your nicotine. Don't forget to drink plenty of water, vaping is dehydrating and you are working out as well, stay hydrated and don't push your self too hard.