Please tell me if it is normal to breathe through mouth and not nose?

Not uncommon: Most patients breathe through their mouth versus nose due to a reduced air passage through their nose (i.e. enlarged adenoids, nasal septum etc...). This brings concern when sleep apnea is associated with mouth breathing. Another concern is that mouth breathing also increases dry mouth which can lead to major dental issues. A physical exam by your dentist or ENT specialist can determine true dx.