Should have the same medical effect - but some have different side-effects. So it could be a different medication.

Having said that, I was on medication for fits, didn't have them for a week (ran out, didn't have time to see the GP for a new prescription, so had to wait a bit) and when I started taking them again I had some major side-effects, and this was the same brand. So it could be change of brand or just sensitivity to the drug, not sure. Go see a doctor about it and see what they advise.