Don't be so hard on yourself. You figured it out.

Sometimes it's hard to tell what's going on with them, especially during the toddler years when tantrums are normal. Also, every child is different. I had DS figured out, but DD was a whole new ball game. It's never ending, even when they get older.
Teething - DS liked to chew on frozen washclothes. I would dampen clean washclothes , fold and put into the freezer in ziplock bags and take them out as needed. DD preferred gummy/chewy and or chilled teethers.