advice needed -19 mo and going to start 5th medication

My 19 month old son was diagnosed with epilepsy at 2 weeks of age. He has been on 4 medicines, that have all worked for a period of time (Depakote being the longest 10 mos.), and then stopped. He has been on Depakote, Tegretol, Keppra, and now Topamax which just stopped working after 1 and 1/2 months. He has undergone long-term monitoring twice and a couple of MRI's. The long term monitoring shows that his seizure activity comes from the right, frontal lobe. The MRI shows that his brain is "normal" in structure. Physically and developmentally he is exactly where he should be, however his seizures will happen up to 100 times daily when they are at their worst. How much longer until this affects him in those areas. He doesn't lose conciousness, and will often talk through a seizure, able to identify people or things around him. His eyes water and his right eye twitches at he end of the seizure I am scared and frustrated, and looking for advice and much needed support from someone who has been/is going through this. Please help if you can!