With people like that, you just have to stand up for yourself and tell her, pointedly and 'nicely'... do not touch my belly I don't like that. Do not make fat comments to me ONLY my Doctor's advice is what counts, stop making harmful comments to me, back off.
Your MIL is just, very very obnoxious and hurtful. You know that.
People like that, bait you, in order to hurt you and insult you.
Their intentions, are not good. It is toxic.
Just tell her "Don't touch my belly. I don't like it." Then move away and put YOUR hand on your belly as a 'protective' gesture.
It is stress, what you are going through... and it is ALL because of your MIL. Your Husband needs to know that. How it is affecting you. And how your MIL is affecting you.
Tell your Husband, "stress" is NOT good for your pregnancy or you.
Just the stress alone and the 'anticipation' of your MIL's reactions and treatment of you... has you all in a stressed out bad mood.
Tell your Husband this. Clearly articulate that. So he understands the psychology behind it.
So he, helps you.
Don't take it out on him. Have him on your side.
It is not him, it is the anticipated MEAN treatment of your MIL... upon you. And she is not nice to you.
That alone, is creating a TON of stress in you.
SO of course, you do not want to tell your MIL about the pregnancy.
You can tell YOUR Mom. Your Mom, is usually the FIRST person you tell. You are her daughter. And your Mom does not attack you like MIL does.
Your Husband, needs to back you up.
He KNOWS his Mom is MEAN. Geez, what a Witch.
I wouldn't want to tel her anything either.
For us, we did not tell family, until I was 3 months.
When/if your MIL asks you how much weight you gained and other pregnancy questions, just TELL her: "That is personal. Only my Doctor's professional advice counts."