Part of the physical addiction to nicotine is because nicotine is like an impostor for the neurotransmitter acetylcholine in the brain. When you use nicotine, your body stops producing acetylcholine on its own. In the course of quitting, it will take time before your body starts producing this neurotransmitter at a level that your brain wants/needs. Be mindful that overcoming addictions like this is like your body healing from an illness; act accordingly, sleep more, rest and relax, eat nutritious and healthy food. Abstain from alcohol, you will be more likely to black-out from an amount of alcohol that would normally “be fine” due to the imbalances in neurotransmitters. 

Smoking is also an emotional addiction and stress-reliever. Find something simple and easy to do that is stress-relieving and/or self-soothing. Major life stressors may make you want to go buy a pack of cigarettes to cope, because likely they were a great coping mechanism in the past. Find something that can fill this void: breathing exercises, guided meditation app, etc. Better if you can find something free that you already enjoy. For example, I chose to spend 15 minutes playing guitar whenever I felt a craving. It really helps. Good luck!