How will I know if I have foetal alcohol syndrome?

Hard to Tell. It is easier to identify in little kids that have characteristic facial features. But as people grow it becomes harder. There is also a range of FAS --- mild to severe. In a way, it doesn't matter because there are no specific treatments. It is probably best to identify which problems you do have & work on them. You should also be aware that you are at greater risk for developing alcohol problems.
Fas. Freunscht et al 2011 examined the biographical development and living situation of 60 adult patients with fas. In their childhood, all the patients had been diagnosed with FAS in a university hospital. Most patients lived in dependent circumstances. The occupational development was characterized by disruption and failure, and severe social problems. So its hard to predict without knowing details.