Speaking personally, I quit smoking just over two months ago. The first two weeks of vaping for me were the absolute worst, but had nothing to do with vaping in my opinion. I say they were the worst because I was coughing up so much crap, it began waking me up at night. I heard a lot of people talk about quitting, or going to vaping, and the effects your body experiences after, but didn't know what to actually expect. Now, I started out on 24 mg because 12mg did nothing to curb my urge initially. At around the 3 week mark, I dropped to 18, then 12 a week later. Two weeks ago I purchased an bigger setup and now I'm vaping 3mg max vg's and feel tremendously better. As far as headaches, I haven't had any to this point. I did just have a dr appt today and my dr pointed out that I seem to have slightly low blood pressure, which would seem odd as I've never had low bp, but in fact, it's always been higher. I told him I quit smoking and started vaping, and he had nothing but praise for my choice and urged me to continue(he also said it's a great step towards stopping nicotine use altogether lol). My suggestion, drink more water and eat healthier. Habits change for some after quitting smoking, and your body adjusts to the change as well. Gotta figure that some people's bodies respond better than others, but, I'm also not a medical professional nor will I pretend to be one. Just my advice from what has worked for me over the years.