Sickness vent and need suggestions

DS started school the middle of February and since that time there hasn't been a day gone by that at least two people are sick in our house. It started with cold and coughs then DS had pink eye then everyone had coughs then DS and I had A stomach bug this week and now DS is congested again and DD is coughing really bad. MIL called me at work today and said that DDs cough is worse and now she has refused a bottle since 9 am this morning. I don't know what else to do. Both kids have been on antibiotics for different things since all this started. We did a really big deep clean, changed the furance filter, I am constantly changing bedding etc.. We are opening windows and doors as much as possible and getting outside as much as possible. Also used hand sanitizer and washing hands constantly. I'm at a loss. What else can I do? What do I do about DD? I hate that she keeps getting sick and I worry about her being so young and little with all this. Urge. I have already used 3 sick days since February and DH has used 3. Help!