Is it normal for my head to swell after radiation therapy?

No. However if your head is noticeably swollen in your face and neck, the doctor needs to evaluate you for superior vena cava syndrome in which the cancer in the chest obstructed the flow out of the neck and head. This can happen even when getting radiation to the chest for lung cancer despite being the treatment for the syndrome as well. Another possibility would be developing venous thrombosis.
No. Not normal for the head to swell, but if you are getting radiation to your brain, there can be some swellling in the brain that is typically treated with steroids.