You can begin giving probiotics straight away, anyway, even before testing, in the case of eczema and other atopia symptoms. Severe Eczema in infants is almost always due to gut flora imbalances. The gut flora of someone that young is affected by
1) birth (colonization by the flora of the mother at vaginal birth, or poor colonization via ceserean, if vag birth and mother has a yeast problem or imbalances herself this might reflect in baby's gut flora as well)
2) antibiotic use (obviously alters gut flora negatively)
3) formula use (when looked at in large groups, breastfed babies have much more beneficial flora and fewer E Coli growth etc. than formula fed babies; studies looking at health differences in groups often have a cutoff of no more than one formula bottle per week - or is it every two weeks, I forget- to be considered breastfed, so strong is the influence of formula on gut flora)
just some considerations. There are lots of good probiotic formulations at Iherb.com. We like the shelf stable Jarrow EPS type with 8 strains, none of them are strep.