Mega emo 3yo boy

[Cheeseismyweakness]

My 3 yo DS is sooo emotional at the moment. No idea why. No Recent major life events; 10 month old brother, I'm back at work as of 2 months ago, 2 days a week.
Cries at the slightest thing- like not being able to undo buttons/ if I try to help with Anything, being left at pre school, little brother touching/using his toys.... the list goes on and on... beginning to think I've damaged him in some way- why is he so insecure?

Possible because you have started back at work? Other than that, my almost 3yr old gets upset when she can't do something, so in some respects that is normal.

Maybe normal toddler-dom coupled with not seeing you as much?