My breathing sometimes gets heavier/harder at night and occasionally, but rarely in day. i had asthma until i was about 14. could it be coming back?

Yes, it could: While asthma can go "dormant" like a volcano, it can return! frequently the symptoms are worse at night, with exercise or with a cold. A simple breathing test called spirometry and if available Nitric Oxide breath analysis in addition to an evaluation by a doctor can assist to determine if asthma is again active or if another problem is surfacing.