I broke my ulna and radius in my arm only amall breaks and due to me being young luckily I only had my full arm cast on for 4 weeks, I have had a it off for 6 days now and the radius seems fine but my ulna is swelled at a point and there seems to be a bit of a bump on it! It also hurts at times but only at the point of swelling and when I do too much with it. I'm really worried and not sure whether this is right or whether I have broke it again, please tell me what you think :)

You should go back to the doctor and have this looked at immediately. That does not sound right and you could need another X-ray to determine what the problem is. This is something that cannot be "diagnosed" over the internet.