Aw, nakaka-worry talaga yan, lalo na kung recurring! A few of us mums have experienced similar rashes sa ating babies, one friend's LO had it triggered by late afternoon heat at sweat, another noticed it was pollen-related kaya nag-avoid ng outdoor time during late afternoon. Since nag-appear usually kapag uwi from outside at nawawala after a week, might be environmental (heat, pollen, dust) rather than food, pero honestly best na i-check with your pedia para ma-identify exactly what triggers it at ma-rule out any concerns, especially since naka-relate sa vaccine. In the meantime, try keeping her in lighter clothing, cool environment, at observe kung ano talaga yung pattern (time, lugar, what she wore, weather) para ma-present mo agad sa doctor. You're doing great tracking it na!