hello there , welcome to HCM, As per your clinical history i suspect oral candidiasis in your case. As the strep test is negative it is not a bacterial but can be fungal infection. white patches around both side of throat are suggestive of candida infection. I would suggest you to start with antibiotic amoxycillin clavulanate three times a day along with some anti inflammatory tablets. Gargling with lukewarm saline water or any antiseptic oral rinse will help in giving soothing effect to the throat. Antibiotics can be taken according to your age and body weight so Consult a physician and get the examination done and start with the course of medication. wish you quick recovery, take care.