Well, considering you have a frequent amount of seizures -- you should not attempt to adjust your medications without first consulting your doctor, since lowering the medication would put you at very high risk for increasing the frequency of your seizures.
It is a bit unusual that you are having insomnia with Keppra -- as the general adverse affect associated with this medication is somnolence - or sleepiness.
Nevertheless, the over the counter medicine that is generally used is something like "benadryl" (which is the medication found in Tylenol PM and Advil PM).
There are other prescription medications that can also help, including some in the benzodiazepine class which may help you -- however this needs to be discussed with your doctor first.
Please don't drop your medication level without talking with your doctor.