It's so hard to not worry! We had a stressful TTC experience so the worry was heightened for me as my DS1 was a little miracle. I didn't do anything aside from waking up, going to work, coming home and resting.
I gained weight, my body stiffened up, I suffered from backaches, severe knee pain (that lasted for months after I gave birth), and felt pretty useless by the end of it! I managed to enjoy my pregnancy once I felt better, but I was pretty lazy...
....and now...I'm pregnant with DS2 and I have no choice but to keep up with my 15 month old who runs around like a little maniac, and pick him up, put him in his car seat, do his laundry, clean his bath tub (and the rest of the house for that matter) and bend down constantly to pick up after him.
It really goes to show how much your body can take - nature wouldn't have it any other way as who else would look after your older children???
Your body has been designed to support a healthy pregnancy, and you can continue doing what you need to (as long as your doctor has restricted something in your life). MC don't happen because you cleaned your bathroom or vacuumed - it is unfortunately nature's way of not letting your body support a pregnancy that has something wrong with it