This is the closest explanation yet, but let me elaborate further:
Anyone who has been smoking for any appreciable amount of time will experience a number of symptoms that take place upon cessation, and these effects will vary from one person to another, regardless of the amount of years that person smoked, and their overall physical health at the time. Even transitioning to another form of nicotine, the body will undergo withdrawal symptoms, and these symptoms can appear very different in different people, ranging from fever to cold-like symptoms to headaches, tremors, sweating. Also, the lungs will also begin the process of self-repair, shedding the damaged lung tissue and tar deposits, so that new cells can take their place. That's why one will often cough up phlegm with tar in it for months after their last cigarette. In nearly all cases, barring severe lung disease or COPD, the lungs will have healed themselves within 6-8 months. It's also the reason why, in most cases, it's never too late to quit and reap the health benefits.
Also, the nicotine withdrawal process can leave some people immuno-compromised for a short period of time while the body makes it's metabolic adjustments. In most people, this only lasts for a week or so, but can be longer or shorter, depending on the person.
Professionally, I won't diagnose you (nor should you accept the diagnosis of anyone other than your physician), but I will suggest to you that, if these symptoms persist longer than a week or so, that you should visit your physician and have him/her check you out.
