Those sayings.. like "1 cart is equal to 1-2 packs of cigarettes" are totally off-base.
You aren't getting near the nicotine absorbed in the same volume of vapor as analogue smoke. A smoked cigarette is much *much* more effective at delivering nicotine to your system... this is for a couple of reasons... first of all the nicotine that is absorbed in analogue is what's known as free-nicotine or freebase nicotine.. free nicotine is able to enter the system much easier than non-free nicotine... this is why you notice cigarettes having a very quick head-rush and why they are very VERY addictive.
Here is a good article on free-base nicotine
Freebase nicotine
The tobacco industry has spent a long, long time perfecting cigarettes into a very effective nicotine delivery system.. one that delivers it almost instantaneously to the brain which in turn increase the addictiveness ten-fold.
Using a PV on the other hand.. we really don't know how much nicotine is actually absorbed. There has been maybe one actual study, and that study didn't bode well (It showed little, if any nicotine being absorbed) but this study is highly contested on this forum, and for good reason. The study used people who probably have no idea how to actually use an e-cig, and they also used a very poor brand of e-cig at low wattage. There has been other small scale tests which give much better results, using people who know how to vape... but one this is for sure;
The nicotine delivery from a PV is NOTHING like a cigarette.
One theory that I think is on the right track is that the majority of absorbing goes on in the moucous membranes, not the actual lungs (as particle size using a PV is quite big) I tend to heavily favor this theory because when I first quite analogues I noticed when I would hold the vapor in my mouth longer/exhale through my nose, I would get more 'satisfaction' from the vape.
One thing that I think is highly overlooked with e-cigs as a way of quitting is that you effectively stop the delivery of freebase nicotine instantly to your brain switching to e-cigs.. this goes a LONG WAY in stopping the behavior patterns that causes addiction. You see, when the nicotine hits you instantly like that, the reward system in your brain gets really confused. Dopamine is released when we do something beneficial (To make sure we keep doing beneficial things) like eating, have sex, etc.. The instant delivery of freebase nicotine from an analogue cigarette effectively short-circuits this system. It causes the brain to equate smoking to a 'beneficial thing' (Because of the release of dopamine instantly after we take a drag) and encourages more and more of it. When you switch to e-cigs, this is no longer the case. You still get the feeling of satisfaction because most of that 'feeling' is hard-wired to the actual ACT of smoking, that's the short-circuit. The minor nicotine withdrawal is taken care of by the low-dose of nicotine delivered by the e-juice. Almost everyone who quits e-cigs after quitting analogues will tell you; It's a thousand times easier.
tl;dr? Don't worry! If you are having negative side-effects from over-vaping, then calm down. If you're experiencing nicotine overdose symptoms, calm down. If not? You're fine! There are people who I'm sure vape much much more juice a day than you and have for a much longer time.