Am I wrong for being upset by this?

My boyfriends mom and I aren’t on the best terms. I don’t like her for a lot of reasons. Anyway, she sent my bf a picture of a faja and said to tell me to get it from her after I have my baby. He showed it to me and said “my mom said you need this for after the baby so she wants to give you this one” I said no I don’t want that. He asked why? And I said I didn’t think it was anyone’s business what I do with my body right after I had a baby, he said well I’m asking, not her. I replied and said it shouldn’t concern him and how would he feel if people were telling him he needed to be skinny and he didn’t say anything. Like who’s business is if wtf I do with my body? And why so much pressure to get my body back? She basically demanded I take it. She always makes comment about me going back to being skinny after the baby and its just annoying. Like don’t worry about what my body looks like after I just had a freakin baby.. smh