My boss is making me feel useless!

Laurie • Our beautiful baby born 18th Nov 2015. Baby #1.💙💙💙
As if I don't feel useless and rubbish enough due to constant morning sickness and now heartburn even after 15 weeks my boss has taken it upon himself to make remarks every time I make an innocent mistake or if I'm feeling sick or even if I feel a bit peckish and it's wearing me down! He's taken away most of my power and authority as store manager already and cut my responsibities to zilch! It's just making me feel so much I worse and I am literally ready to walk away but I can't!! I can understand if I wasn't a hard worker but I have always pushed myself, always been there to do the job and always done it properly and I know I have to cut down how much stress and work I put on myself but this is ridiculous!! I also can't stand the humiliating me infront of other staff members if I've made a mistake and comparing me to them infront of them! 
I don't know if I'm being petty and emotional and jealous that I have to eventually hand over my job when I leave for maternity and I'm struggling or whether he is genuinely being a dick!!!
I'm only 15 weeks I've still got over 5 months left of work!! I am fully capable! 
TEARING MY HAIR OUT! 
Sorry if none of this makes sense I'm ranting and just so fed up!