I had covid-19 1st time before vaccines exist, i didnt get any symptoms at all. now i have it 2nd time after vaccinated all shots including booster, im having mild fever, sore throat, headaches and tiredness, how is that possible scientifically ?

Symptoms can vary widely from one infection to the next. Possible explanations include the dose of virus at the time of infection, the particular strain of COVID virus, and simply random luck. But this is entirely normal and nothing to worry about unless you develop severe symptoms, like bad cough, chest pain, or shortness of breath. See a doctor ASAP if any of these symptoms appear. Good luck.