Just wonder how long does the effectiveness of the brake paste lasts?

Initially, my brake squeked frequently, when I applied brake from a slow speed. After applying the brake pad paste (cost a bomb in Malaysia US2.65 per paste, if compare to partshop price of US$0.70 ) it worked for about a month or so. Now, the squeking sound is back

My brake pad is original MB, by Textar.

Any further recomendations? Maybe I should also check the disc, like what Ashman has encountered

Thanks

Lim