Hatha Yoga is a NO PAIN, NO PAIN Yoga. Not like any fitness program you've done in the past "no pain no gain".
If you begin to feel any pain or discomfort with Hatha Yoga you should back out of the pose, modify, or skip the pose if you can't resolve the pain or discomfort issue. It's ok to test the stretch but listen to your body. Start slow and work on form before taking yourself to your comfort edge. DON'T FORGET TO BREATHE.
To modify you can use Yoga props like blocks, straps, bolsters, and blankets. If you are at home and do not have Yoga props, use whatever is available around your home. Such as couch, chair, belt, blankets, sofa cushions, and whatever your creative mind can come up with.