Toddler Suddenly Aggressive

My toddler (2.5 years old) has suddenly become aggressive to other kids at daycare and has become almost uncontrollable at home. Dad just recently started a new job where he is in training Monday-Friday and is not home (i feel like this is when the major issues started). I’ve noticed our sons attitude change a lot. He no longer responds to me at all and will look right at me and do exactly what i say not to do. If I try to discipline him with time out or taking away toys he has a complete meltdown and starts kicking and screaming. He’s recently starting pushing and kicking other kids at daycare multiple times in a day. I am at a loss on how to handle this? I don’t want him to hurt himself or others. It’s really worrying me. He’s never been aggressive like this or been this defiant. It seems like he doesn’t listen to me at all, when I know he understands what I’m saying. Any ideas?