Marilu - I am not sure of your situation, but if your LO is really struggling with illnesses and you are paying a ransom in doctor's bills and medication, it might be time to think about switching to a full time maid and have your LO stay at home for the next year allowing the immune system to recover and start building itself up.
I took my first child along to a creche and then ended up at the paed every second week, finally when we were admitted to hospital for yet another lung infection did my wake up moment come along. I found a full time nanny and had my son at home until he was about three years old. (I thought I could not afford it, but realised that it was not as expensive as I had thought and had tons of other benefits.)
With my 2nd child I learnt from the first and kept her at home until she was about 18 months, and then found a school that the nanny could walk to. So my daughter went to school part day, and if there was a hint of a runny nose she stayed home. She never met her paed after her 6 week check up as she was never ill.
3rd child - a year tomorrow - at home with nanny. Never been to a paed, been to a doctor twice in her life for mild issues that I wanted a 2nd opinion on.
I am probably going to start her at school at 18 months on a part day basis.
If there is any way you can afford a full time maid to stay with your LO, I cannot tell you what a difference it will make to your sanity, your doctor bills and your sleepless nights dealing with a sick child.
Just thought I would put that out there ....