Cancelled Plans. Looking for advice.

It's mother's day and I woke up in extreme pain. I'm thinking of cancelling on my mom and rescheduling.

A thing that's bothering me though, is that I told my boyfriend I'm in pain and instead of immediately understanding, he just said is it because you don't want to go? Or is it because you're actually in pain?

I am actually in pain. I'm constantly in pain. I just started with a new specialist and started a new preventative, but don't have my emergency med yet. I don't think he understands and I don't know how to make him understand. It really messed with me today because I always feel awful cancelling plans.