My baby is sick…again!?!

The last few months it seems that my baby is getting sick. He had a cold for several weeks and a fever. That would start to get better, a double ear infection that didn’t go away with regular antibiotics so he had to get stronger medicine. That got better. He got a cold again only a few weeks after this and it just seems to be lingering now. That appeared to be getting better. He had his surgery for his hydroceyle and circumcision. Now it’s like he is sick again the day after his surgery. Cough and cold came back. Now about a week later after his surgery he’s running a rectal temp of 101.9 and I don’t know why he’s just getting sick so much! I thought breast milk was supposed to strengthen his immune system. I gave him that for like 5 months!?!!!