Yes, you can do this to reduce the frequency of periods, but it's probably a good idea to have at least four periods a year. In the US, there is an FDA-approved pill (Seasonale) that is packaged so that you get your period once in three months. Not sure if it is available in Singapore.
I take my low dose (same dose in each pill) pills for 7 weeks straight, then stop for the 8th to have my period. I have tried stretching to three months, but I started spotting at around the 8th week, so I stuck to the two month schedule. There was another time I stretched to three months because of a vacation, and that time I didn't have any breakthrough bleeding.
I haven't experienced any adverse effects. The only problem is getting enough pill packs a year. Some doctors won't prescribe more than 12 packs a year, or insurance won't pay for more than 12. It's easier in Singapore, since you can walk into any GP and ask for pills, which are cheap without any insurance. You could go to two different GPs to get enough pills, if you encounter conservative/resistant doctors.