I dont have chest pain but on my left side there is a dull ache that comes and goes. ?

Aching sensation : There really isn't enough information to even gander a guess as to the source of your left sided ache. Be well.

Muscular: This could be minor muscular strain. Be sure to look at your posture especially while sitting to do work/at a computer or on a mobile phone. Try different positioning while doing activities. If this worsens or doesn't improve or if new symptoms develop, please see your doctor for a comprehensive evaluation.