My bitch that is expecting has been groaning or grunting almost her entire pregnancy. She didn't do this for her first litter. I haven't seen any other signs that something is wrong. She still has a few weeks to go. Should I be worried?

If she is far enough along to do so (28 days), get an ultrasound. And just for peace of mind, have your vet check her over also. It may be that she is feeling pressure on her abdomen or diaphragm, or there may be a problem. It's always best to know what's going on if you see any unusual behavior.

She had an ultrasound about 2 weeks ago, nothing abnormal.

The first litter she did not know what was going on.....this time she wants
to make sure that YOU KNOW what's up because SHE KNOWS......SHE IS HAPPY AND VERY PROUD OF HERSELF! Enjoy and talk to her about her pups....of course
rub her belly and she will (talk) even more.