Actually, skahn47, many people who get hit by side effects from CK get them in the first two weeks following treatment, although this is usually limited to fatigue. The first four weeks after treatment were the very worst for me, by far; I was so fatigued, it left me short of breath and struggling to even sit up straight in a chair (although it must be said this was a particularly severe and unusual reaction). It seems like it's pretty common for people to also have an extended episode around the 3- or 4-month mark, too.
On the plus side, a strong reaction isn't necessarily a bad omen. It could mean the tumor is reacting very strongly to the radiation and is on its way to the grave. That was certainly the case with me. My tumor initially swelled significantly, only to shrink at an almost unheard-of rate.
I hope you feel better soon.
Best wishes,
TW