people used to tell me that to, my theory was im pregnant not sick, i am healthy and had low risk pregnancies and part from morning sickness i was fine. Your body will tell you when you need to rest, ( and it is important that you do rest sometimes )we were renovating when i was pg with DD and it got to about 32ish weeks and i said to my DH that i just couldn't do as much to help anymore, especially lots of bending etc. you need to be careful of lifting and shouldn't be up and down ladders etc. but as long as you feel fine in yourself then keep going as you are.
I don't know about stats etc about activity or too much activity bringing on pre term labour maybe someone else can shed some light on that, but if you are normally, fit and quite active and your body is used to that kind of level of activity you should be fine.
Enjoy the rest of your pregnancy and try and get some rest sometimes you don't need to be super woman