Hi David-
I had surgery + radiation only. I think I had XRT, not IMRT so maybe my experience was different, but I'll tell you how it went.
Around week 2 I lost my taste buds but felt fine(except being tired). Around week 3 it started hurting more and the vicodin I was taking didn't cut it. They experimented with morphine to find the right dose which made me throw up alot. Then they put my on a arm patch of fentanyl which worked well to control the pain so I could keep eating and drinking. I only eat liquids(mostly ensure and carnation instant breakfast). Around week 3 I developed a bad tongue ulcer(due to not putting the cotton pads in the right place to protect my tongue. That's why I stopped eating solids, becuase my tongue hurt too much and then even with the pain meds I would bite it accidentally.
I could drive myself before I got on the fentanyl which was nice. About halfway through you develop mucositis, which is where you get mouth sores and lots of mucus as your body tries to fight off the radiation. Have lots of tissues around for spitting out loogies! As treatment went on, I didn't like swallowing and I wasn't drinking enough water so I would periodically go in and get fluids in an IV. The nurses keep a good eye out for that.
As for the constipation, the nurses should give you a list of daily stool softeners or laxatives so it doesn't become a problem.

Sigh....it sucks but you will get through it. Today is my last day "hooray" which means then next few days will probably be really lousy.
So, check in often when you need support. I found that some days I just needed to hear someone else say that they had been through it and are now fine.
Melissa