Working in yard

Hey.. Me and my fiancé had a ton of trees cut down in our yard.. Now we are trying to clean it up.. Anyway I am almost 22 weeks pregnant and am having a hard time helping him.. I either get so hot I puke or I just feel like I can't get air. Is this normal? Do y'all think it is okay to help pick up the limbs and burn them? My fiancé don't see why being pregnant makes it any harder than not being pregnant.. Which is a little frustrating.. If you are pregnant would you be outside doing this? 
This is what we are doing and OMG we have so much more left to do..