I get throat tightness in a an air conditioned places, often in trains and buses. That happens on humid hot weather. Could I be allergic?

Not necessarily. The fact that this happens mainly in tight or crowded space suggests that this may be related to anxiety or panic especially if you are claustrophobic. Another condition is vocal cord dysfunction in which the throat closes up when you breathe in. Consult an ENT if this is troublesome to you.