Yes, there's a whole lot more to the radiation than just those symptoms. The anus itself, if not protected vigorously, will not just get red but develope some serious problems. You must remember that radiation treatments will dry and thin the skin out. While on the surface that doesn't seem to be that big of a deal, it can and does burn the skin. The tissue around the anus itself is extremely delicate and thin to begin with and the damage that is done from the treatments themselves really take a toll. The anal tissue thins even more, can and does become very dry and begins to develop thin fissures - much like paper cuts. If you live in a dry climate, you might notice in the winter that your fingers get little painful 'cuts' in them. This is much like what happens around your anus due to the treatments. Once these fissures occur they can be very painful. Every time you have a BM they stretch or break open again causing a lot of pain since the nerves in that area are quite ample. Even with meticulous care, you can still develop these fissures. You need to wash with a gylcerin based soap to help avoid any more dryness (regular soaps, even Ivory or Dove tend to dry the skin out), use aloe vera liberally over your body from about the waist to the top of your thighs, and find other products that will help keep your skin moisturized - INCLUDING the anus itself- but that don't contain alcohol. Remember that alcohol also dries your skin out.
As for the diarrhea, you should have been told what foods to avoid eating to avoid this problem. Remember that your intestines are also being affected by the radiation and are becoming very very irritated. Foods such as: fresh veggies, fresh fruits (except bananas), whole grains, nuts, popcorn, spicy foods, etc. are very difficult to digest and will only worsen the digestion issues. Instead you should eat easier to digest foods such as: chicken, turkey, beef, cooked veggies (in moderation), coooked fruits such as applesauce (I also went and ate baby food pears & peaches), white rice (not brown), potatoes, pasta. Some people have difficulty with dairy products while others don't.
The chemo and the radiation are also killing off the good bacteria that your intestines need for digestion. It's important to take a probiotic to put that good bacteria back into your system. The problem is that even those get killed off but at least you can hold the diarrhea at bay. I took a probiotic called Sustenex because it doesn't dissolve until it hits the large intestine. Twice a day, every day and I kept the gastro issues away.
You should try to have your treatments done with a full bladder. This helps on a number of fronts. The full bladder helps to push some of the intestines out of the radiation field and spares them more damage. It also helps to lessen the effects of the treatments on the bladder itself which will be important down the road. Most patients find that after treatments are over, that they have some bladder issues. These can range from incontinence to simply having to go more frequently.
It's also very important to remain hydrated - and I mean REALLY hydrated. While the docs told you about the diarrhea, I am guessing that they didn't tell you about the very real possibility of radiation proctitis which can rear its ugly head years after treatments are over. Hydration can help with this. Keeping liquids in your body not only helps you just feel better, but allows your internal organs to not take the full effects of the treatments which is important later on. Just like we pour cold water over a burned finger to stop the burning effect on the skin, so should we keep ourselves hydrated to stop the internal 'burning' effect on our intestines, bladder, etc.
Please forgive me if you have mentioned before whether or not you are male or female, but there are big time issues with radiation and sexual function that I am guessing weren't mentioned to you. As a female, I can't speak to the male issues, but know that they do exist. The female issues, however, are a HUGE problem with scarring/adhesions, etc. in the vaginal area and lead to a closed vaginal canal if care isn't taken to keep it open.
It's been my experience from listening to literally hundereds of patients undergoing pelvic radiation (for prostate, rectal, cervical, uterine and bladder cancer) that rad oncs just seem to gloss over the problems that go along with these treatments. It can range anywhere from the 'don't use anything on your skin" (WRONG WRONG WRONG ) to the absolutel denial that anything will happen to the patients. Please, I don't know how far along you are in your treatments, but know that there will be problems and you need to start taking care of yourself NOW before things get any worse. Feel free to PM me if you feel you want any more info.
Jaynee