3months feels like something stuck in throat no other symptoms is this a common sign of mouth or throat cancer? Smoker. Neg CT scan of soft tiss neck

Many possibilities. That symptom is very common and could be associated with many things. It appears that you don't have an enlarged thyroid gland or other mass because of the ct, making cancer unlikely. It can be related to acid reflux(gerd) and laryngopharyngeal reflux(lpr). Some people require mo's of twice daily reflux meds to help. Another issue can be muscle tension dysphonia, so see an ent/laryngologist.
See below. You are very young age wise to get a smoker's cancer ordianrily it takes at least 20 years. So the thing in your thrat may be an irritation from something you ate or in fact the smoking may cause you to feel this way but it is not cancerc.