What would you do? Work related

I am a supervisor for an after school program. I'll be 29 weeks tomorrow and part of my job includes walking around a lot, and lately I've been getting sharp pains when I walk too much. My boss said " I know you're pregnant, but you need to be more involved." 
1. He's never there to see how involved I am
2. Is that not a form of discrimination? 
I'm just so annoyed with his comment