So I'm only 4w6d preggo but was curious: what kind of activities does a pregnant woman need to avoid?

My husband who usually does all the "manly" stuff around the house hurt his back and can't do ANYTHING. We live in the country so our 2 acres needs to be mowed... normally we both get on our riding mowers and do it but now it's just me! But I've been doing all the lifting, moving, etc.

He got hurt 4/19 and I got my bfp 4/28.

I'm a big girl, 5'11" 265 pounds.. I'm tough, BUT I had a miscarriage in February and I want to do everything right this time!

So my question is, what activities should I avoid? I know they say heavy lifting, but what constitutes heavy?!?! And how do I ask for help when no one knows I'm PG?!