The last 4 days i have sourness. usually, when i eat, i feel better. what could it be and what i should do?

Sour taste in mouth: Suggests acid reflux. Cut down on intake of coffee, soda, spicy foods, tomatoes, oranges etc. Take otc Omeprazole and antacids. See your dr if symptoms worsen. Take care !

Heartburn?: If you're describing sourness in back of your throat, what's been described as "brackish" taste, you might have heartburn or reflux. Here in the states, you can try over-the-counter h2 blockers like ranitidine, etc. Even mild proton pump inhibitors are available w/o prescription. Or simply calcium carbonate like tums. Best to go see your family doctor if this continues.