Xolair; can anyone explain their experience with it?

I am going to have my first Xolair injection on Monday for MCAS, would anyone be able to tell me their experience with it?

I'm curious if anyone had any reactions, positive or negative.

If positive how many injections until you noticed a difference.

My last question, is has anyone gained weight on it? I have gained 47lbs in 3 months and scared to gain anymore. I used to be 95 to 100lbs now, I can barely walk due to the inflammation and joint pain.

I apologize if these questions were already asked. I did not see them.

Thank you.