Heavy lifting airport job while 10 weeks pregnant!!!!

I work at the airport for the airlines and today was my first day back to work after a month (I had very bad morning sickness) I decided to go back today and now I feel terrible. Idk if it's from waking up at 5 in the morning or me being off for a month but leaving work my feet hurt my head hurts and when I walk my legs and pelvis hurts!!! I don't want to be a big baby because before I got pregnant I could do this job with ease... Now the thing is I tell my managers that I have a doctors note stating I can not lift for long periods of times but no one will take my note... I think they just don't want to lose out on an employee but that's just my thoughts! I want to know is it even safe to work like this?