Rectal narrowing and spasm

I’m a Crohn’s patient on Remicade every 8 weeks and suffered before from a perianal fistula. Since last November I have had rectal problems including rectal pain and soiling. I underwent an MRI dynamic which did not show any fistula. Rectal pain has been persistent ever since. My GI literally tried every possible rectal med out there. I saw him yesterday complaining of this severe rectal spasm and severe abdominal cramps that would last for 15 minutes after a bm to the extent that I would fear having a bm though I have diarrhea all the time. I reminded him of the rectal narrowing I had before and he refused then to do any kind of dilation. He recommended adding Pentasa (mesalamine) enema 4g to be used one night and Trud enema the other night and to take Imuran again.
Does anyone have a similar experience? Today, is the first day for taking Pentasa enema 4g and I feel very much exhausted. In the past, I used to take 1-2 gms but this 4g enema causes fatigue. Is this normal? Are there any pieces of advice I should follow to be able to insert the enema without having pain. I do lubricate the enema nozzle but I have a problem with my tight rectum.