I think its a big transistion to having a Carer and going to Day school, is there any way you could cut down on the Day care? It does seem to come from being there , hes not getting one to one care now either,Hes only 2 he needs Mom around more if it is possible.Your Doc will tell you if there are any effects from the Fever he had.
Did your toddlere first get sick at the daycare? If so, he may associate that feeling all over again with being there.