Spring Cleaning (not really, just cleaning while it's Spring)

I've been doing a lot of sewing, (like this, this, this, and this) and all of a sudden

I was wondering why my tension was off, 

and why my stitches looked like poo.

Ethel, my workhorse. 

Maybe because of this...

bobbin case

or this...

Or all of the above? 

Yes, yes, and yes.