Sharp stabbing pain under left ribs/breast could be due to acidity with gastric reflux or hiatal hernia. 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, carbonated drinks and spicy food. Walking around also helps clear gas. I would strongly recommend you to see a gastroenterologist (a specialist who looks after the diseases of our digestive system) if these tips help you.
Other than that it could also be costochondritis, pleuritis (inflammation of covering of lung) or pericarditis (inflammation of covering of heart). Since you do not mention any other symptoms, it is less likely to be any of these. IBS, Crohn’s, chronic constipation, spleen problems like bleeding, cyst, abscess etc can also cause pain under left ribs/breast.
Please consult your PCP for primary examination followed by proper referral. Take care!