Normally with an infection (like the flu or something) then you would wait a week or something. But with abscesses and stuff, it's the Crohn's itself that is causing the problem. Get rid of that, and then you'll be able to use antibiotics to help fight off those infections.
I've had two c-sections, and both times I had Remicade a day or two after. I've gotten them with colds and stuff.
"For this thing I besought the Lord thrice that it depart from me. He said, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities; I take pleasure in infirmities, reproaches, necessities, persecutions, distresses, for when I am weak, then am I strong" 2 Cor