My two cents:

Having been on the other side of the hiring process a few times (not the boss but the notetaker), there could be a few reasons why you failed to clinch the job at the last round. The few times that my bosses were not keen on hiring someone is due to the "attitude" that the candidate showed. All things being equal, employers are more likely to hire someone who is willing to admit they do not know everything and who displays a keen and willing sense to learn, unlearn, and relearn. What turns employers off is those who pretend they know everything and try too hard to impress. Having a sincere and humble attitude often works, especially if one doesn't have much working experience in the field one is applying in. Show that you may not know all, but are willing to try to find out from others and learn. The point is that if you do not display the right attitude during the interview, chances are you are unlikely to fit into the office and team culture and will be more trouble than you're worth. Especially in the civil service, the ability to be a good team player is very crucial.

The other reason could be that the places you applied to are simply very competitive so the employers have the luxury to pick the cream of the crop. In this case, take it in your stride coz there will always be someone better than you so don't take it to heart.

Sometimes, timing is another factor too. Between Mar-Jul, there are many fresh grads competing for jobs, so the playing field is definitely more crowded. If you can afford to wait, try the "off peak" period from Aug-Feb where the competition may be less keen.

Keep trying and all the best!