When I started vaping, I went through some mild withdrawal for 2-3 weeks, and I do think it was from the other chemicals in cigarettes. It's my understanding that many (all?) of those chemicals were added to keep you hooked on cigarettes, so it makes sense. Knowing I was still getting my nicotine was a comfort and got me through it.
I took 10 or so days of dual use, cutting back my smokes more each day until I was down to none. I had to have that bit of security, rather than just stopping all at once. The hand to mouth action that vaping provides pretty much took care of any psychological factors for me.
Yes, it is possible to get too much nic. For me, the symptom was a terrible headache, but others have reported other symptoms. If you can give more details, like how much you smoked, what gear you are using and nic levels of your e-liquid, that might be helpful in determining what is going on.