I can understand that you would be worried. More than 1 fit in the span of several weeks is definitely cause for concern and should prompt a vet visit ASAP.
There are numerous reasons for fitting in cats such as metabolic disease, toxicity, epilepsy or a brain tumour. Many causes are treatable, however, without appropriate treatment, your cat is suffering the exhausting effects of seizures that are very likely to become more frequent, longer lasting and even lead to death if left untreated.
Unfortunately your cat needs to see a vet for this condition. The good news is that there are now many charity organisations and funding plans which help owners, such as yourself, provide much needed treatment for their sick pets.
Ask your local vet for more information on these options and best of luck getting to the bottom of the problem.