I'm not understanding the system.

I'm Diamond 1 and today I lost one game and lost 20LP

The next 3 games I won.

First Game: 3+LP
Second Game: 3+LP
Third Game: 1+LP

Riot Pls?

EDIT: Yea I didn't think the picture would be that small lmao.

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I can't make out the numbers on that pic (microscope), but one of 2 things is happening:
1) LP clamping - you are gaining very little LP per win because you are close to 100 LP and the system wants to make sure you earn that climb to Challenger.
2) MMR is low - you have a lower matchmaking rating than is expected in Diamond I, and as such, you are gaining less LP for wins and losing more for losses.

It's probably the first one, considering you made it to Diamond I.