Hi! Many thanks for your question on eHealth forum!
Any pain in left side of chest should be investigated for angina and heart disease to be on safer side. Hence you must get a 12 lead EKG while you have the pain.
Since you smoke or smoked, have an IUD and had a pregnancy, you could be having acidity with probably GERD or hiatal hernia. This can also cause a left side chest pain.
Take a late night snack. Raise head end of bed. Take Omeprazole empty stomach in morning and an antacid gel at bedtime. Refrain from smoking, alcohol, fuzzy drinks and spicy food. Maybe these tips will help you. Since a confirmed diagnosis cannot be given on net please discuss these possibilities with your PCP and get a referral for a gastroenterologist.
Pericarditis (inflammation around heart) and pleuritis (inflammation of covering of lung) is also a possibility but with your long standing history quite unlikely. Hope this helps. Take care!