Most people get pre-meds before their infusion in order to prevent any reactions (regardless of whether or not they've had reactions before). Maybe you should ask your GI about
that, especially since you did get a headache afterwards.
I tried several types of probiotics when I was flaring, and none of them made a difference on my UC. However, I have IBS on top of UC, and VSL #3 helps with that. You don't need a prescription for VSL#3--you can order it online (just google it). If you want the strong version, VSL #3 DS, then you need a prescription.