Toddler hitting me

Hi ladies
My normally calm and happy toddler (2 1/2) has reacently started hitting me when he gets frustrated or when I make him do something he doesn't want to like get dressed etc
I've normally always been able to stay calm when I discipline him and tell him no but nothing I have tried is making him stop and I am at my wits end with it.
I've tried ignoring it, time out (used to work but now he laughs and runs away) I've explained that hitting makes me sad and he normally cuddles me and says sorry ( but will still do it again and again) Ive yelled ( which I hate)
Any advice would be greatly appreciated I'm hoping it's just a phase but It's a really horrible one!
Thanks in advance