Antibiotics for ear infection---18 month old

My 18 month old son has a double ear infection with the left being worse than the right (it's crusty). He's been exceptionally cranky lately and I finally realized that it isn't just his teething and took him to the doctor today. She prescribed him Amoxicillian oral Antibiotic to take 2 times a day for the next 10 days. This is his first ear infection and he has never been on Antibiotics before. He is also un-vaccinated. I really don't want to give him the Antibiotic but part of me feels I need to. I did give him one dose so far. She also gave me some numbing ear drops to help with the pain. My question is do you think this one course of Antibiotics will disrupt the good bacteria a lot or should I not be too worried about it? I will most likely give him probiotics afterwards. What do you all think? Thanks so much!!

Nicole