Could The Bruising On Arm Be Due To Damage Of Ulna?

Hi - i fractured my ulna in september and had a full cast on my arm until mid december, i was told not to play sport for another 6 weeks to give the bone time to recover, since then ive been back training for a few weeks and knocked my arm yesterday, at the time i did not feel muh but today i have started to feel bruising around the area which was fractured and it is sensitive when pressed against objects, is it likely i have re-damaged my ulna or could it just be temporary bruising? what should i do?