Where I live schools advertise on the LA website. There is a section for TAs and about now is when there will be a zillion adverts, well not quite but certainly lots. Errrr you have GCSEs, A-Levels and a degree, how is that 'no qualifications'? You also have 4 years of experience. You have heaps more than a great many people applying to be TAs. Stop being so modest and worrying about it and get applying. You are likely to be snapped up in no time. You aren't near Oxford by any chance are you?