I'm having a strange issue. My looking around movement has became very jagged and when I look up its very slow. Look up and over is jumpy.

I played a few days ago and it was fine. I hadn't change anything but adding in a few mods, so my setting as I had them worked then.

I tried turning settings down, turning off v-snyce.

Nothing seems to work.

Can a mod cause this?

My fps is fine, it stays at around 30.

Which new mods did you add?

30 fps (average) is inadequate.
You will encounter minimums below 30, which you are describing...