
I would speak to the vet as he needs to be calm hence the medication, as has been already said dogs reactions will vary, normally the dose given is too high and needs reducing but sounds like your dog isn't getting enough,how much were you told to give and how often, maybe with your small breed the vet has been overly cautious in the recommended dose, they should be able to tell you over the phone what to increase it to avoiding taking a trip to the vets.
I am surprised that the vet gave him vacs with the recent history of a seizure as they can mess with the dogs system, making it harder to figure out the trigger.
What was he doing each time the seizure happened? Sometimes it is triggered by some activity, have you changed his diet recently, could he have banged his head,could he have eaten something poisonous to have started suddenly having these seizures? Is the vet going to investigate further, blood tests etc.?
My Mum's dachsie Penny has seizures following surgery for a Liver Shunt at 8 months old, it is thought that her blood got so toxic it caused brain damage, hers are triggered by getting over excited so we try to keep her calm, they happen rarely and vary in length, she isn't on medication for them as they dont happen very often,she has only once passed urine during one, she is very quiet for about 12 hrs afterwards but is back to her normal self the next day, she was 9yrs old last month.
Just keep calm,talk to him quietly,keep him cool[the body heat can rise very high,laying him on a damp/wet towel or laying one over him may help if the weather is hot] in a darkened room till he returns to normal
I hope the vet can get the dose right for you and it does control them.