Is there a way to tell if my radiation therapy is working?

Not always. This depends on if you can see or feel the cancer physically or your doctor sees the tumor on setup x-rays. In these cases you could see the tumor shrinking and as such it is working. In many cases we are treating cancer that are too small to see even on x-rays and the therapy is based in studies that have shown radiation will work. Over time you are examined and xrayed to verify how it worked.
Yes in selected case. During treatment for pain palliation for example, symptom relief is a good sign that radiation is working. We can sometimes see tumor shrink during treatments on images we get during treatments, like a lung cancer. In many cases though as dr kamrava stated, we have to wait to see response at least a couple of months out from treatment.
Not really. During treatment weekly or sometimes daily films are taken however these films are used to verify your alignment and not really for monitoring your response. Most typically you have to wait until after treatment has been completed and then have imaging studies and/or a physical examination to gage the response that you've had to treatment.