Worried Mom...please help.

My 7 year old son had his first seizure while he was with my grandmother almost 3 months ago. She rushed him to the er and he was vomiting many times. 2 weeks after his first seizure I took him to a neurologist with high hopes since he hadn't had another seizure. The doctor recommended my son be sleep deprived for the eeg test. My son went to sleep during the test and upon waking him he had another seizure which would be the second. The doctor diagnosed him with epilepsy. He started Trileptal for 30 days but broke out in rashes. Now he is on Keppra and he's been fine. There hasn't been another seizure in over 2 months. I've been having trouble coping. Recently my grandmother slipped and told me my son had fell out of the car but she immediately cleared it up saying he almost fell out of the car. It was very shocking for me, now I believe my son had a head injury that caused all this and my grandmother will never admit it because she scared I wouldn't let her keep my son anymore. I don't know what to do. Or if it being a head injury would it change the diagnosis of epilepsy. My son had a normal mri but I'm still so concerned and worried. What would be your next step? Has anyone been diagnosed with epilepsy because of a head injury?