I think a low grade fever is pretty common for us Crohnies. I'm usually over 99.5 in the evening, it's just my normal. You could give them a heads up though, but mention it's not new.
Two months is a long time, maybe you should talk to someone. Fever can be your body fighting off inflammation. I seem to get low grade fevers when I'm flaring. Do you have a nurse or nurse practitioner you can call?