And I don't know if I'm going to survive!

I had a pretty mellow, laid-back easy baby. He napped well, ate well, rarely cried and omfg, he's gone.

My toddler is fearless, stubborn, has a huuuuge mommy preference, and has been just rotten lately.

I love love love my son but holyyyy cow! He screams if we take something away, he's started straightening his back if we try to sit him in his high chair or car seat (he wound up getting his head bonked in the car because of it and it broke my heart!). Diaper changes are a huuuuge battle.

I realize this is common toddler stuff but I'm looking for advice on discipline. In my mind, he's still a baby and I have a hard time correcting him but I need to start working on gently guiding his behavior.

Any suggestions or resources you found helpful? We are against spanking and want to avoid yelling so we are currently trying to be stern and say no, then explain "we need to sit in our seat" or whatever the situation is. So far, no dice. He just laughs or screams.