I think it should be worded carefully on how safe, exactly, vaping is with the use of nicotine. Undoubtedly, there are studies in the works as to how safe the use of nicotine through these products is. But, something to maintain, nicotine is in no way completely safe for the body.
The key term, until proven otherwise, should always be harm-reduction. Not elimination.
Per the OP's issue. As many of said, your need to consistently feed upon your pv is an expected result in the transition from smoking cigarettes to vaping. To say that it's completely safe to do so, meh, I wouldn't go as far to say that. However, I would definitely wager to say that it sure is a hell of a lot safer than smoking, without a doubt.
When I first started vaping, I used a super potent menthol, at 24mg. It was so strong, that even when I tried to chain vape, it made me set the ego down every now and again, hehe. Once again, to reiterate as others have been saying, stick with it, you'll find your niche. Best of luck to you, I wish you well and good health.