From your history it looks like the syrup caused the black staining on your teeth. The yellow color in front of some teeth may be calculus or tartar due to lack of dental scaling done
Next Steps
Next step would be to get the teeth cleaned once by a dentist once clinics start functioning normally
Health Tips
Please don’t need to be alarmed as these stains are removable by scaling by a dentist , for the time being refrain from taking the syrup if not needed. DO NOT use home remedies like Sodium bicarbonate and lemon juice as these will only damage the enamel layer of your teeth