FPS bug that's probably caused by a RAM issue

So this bug happened when I played with 1.7 or higher. I put the render distance to 16
and the fps went down to 0 (I usually got about 180 fps). Then I tried OptiFine and that kind of lag stopped but about every 5 seconds the screen stopped moving. (this happens when the RAM is at 100% and some stuff gets deleted). My username in Minecraft is drohne22 if that helps.