M.M.
Oh I know what you are going through! The only advice that I can give that worked for me was you have to be consistent and follow through! I'm sure you are already but just like potty training, persistence will pay off in the end. Also, for whatever reason my DS would really calm down during a tantrum when I asked him if he wanted a hug. His answer was always yes. This may or may not work for you, but it's worth a try. When he would hit me I would look at him straight in the eye and very sternly say "You are not being nice to me right now. Please let me know when you can be nice and I will play with you again". Worked like a charm.
Your DS is growing up and there is so much going on with him emotionally. Be patient, kind and loving. That he is clinging to you while you are trying to get ready for work tells me he needs you more than ever right now. Of course he doesn’t want Mommy to leave but maybe he is having a hard time expressing that?? His little world is changing so much in his mind that he needs you to reassure him.
As long as you are consistent, this will pass.
HTH