Everybodys ranking is 'reset' to 0 at the start of every month. So that means that you don't lose your points that you have collected in last month, they show up in your game history, but you will start again at 0 at the start of a new month. This way you collect points for every month and for the whole year as well. The points in the ranking lobby shown beside your name arefor the current months points only.
When you enter the ranking lobby and click on your own nickname and a chat window will open. Click on the flag and a new window will open & show you the last games that you played, (the one with the yellow date), click on that, then you will be able to see your own monthly points for past months and at the top the points for the year and under that the last games and there ranking.
The change from one month to the next one is based on timezone GMT+1, as this whole AsoBrain site is based on this time (for the reason that the owners of this site does live in the netherlands). You are able to see this time at the frontpage; it is the time shown up at the clock for Amsterdam.