@visitacionmouna Lichess uses the Glicko-2 rating system, which is basically the newest and most accurate rating system created. Read more about it here:
http://www.glicko.net/glicko/glicko2.pdfIt's a hefty formula, so I would applaud you if you could understand it, as I don't completely understand it myself. Essentially, your complaints about varying rating changes probably stem from your rating deviation (RD). A lower value means your rating is stable, and is subject to smaller amounts of change, while a larger value means the accuracy of your rating is uncertain, thus increasing the amount of change per game. For reference, an RD of 45 is the minimum, or most stable, and RD of 110 means your rating is provisional (has a "?" next to it). Looking at your profile, your Atomic and Racing Kings ratings are stable, while your other ratings are not. Therefore, your Atomic and Racing Kings rating should change by smaller amounts after games, while your other ratings for other variants will change by larger amounts.
Another thing to keep in mind is that your opponent's RD also influences how your rating changes. If their RD is high, your rating will change less because the accuracy of their rating is uncertain, so their rating might not match their skill level. If their RD is low, your rating will change more. If you play players with provisional ratings (have a "?" next to their rating), your rating will change by a smaller amount than if they don't have it.
That's a brief explanation about your complaints, read the Glicko-2 paper if you want to understand more. I'm just glad that Lichess has 1. an effective anticheat which has been praised by USCF (
new.uschess.org/news/us-chess-endorses-lichess-fair-play-methodology) and 2. an advanced rating system which is more accurate than any other chess website or chess organization (
lichess.org/page/rating-systems).