Tight hamstrings (muscles at the backs of your thighs) can cause lower back pain. As the hamstrings contract they tug on the lower back area, causing strain and making it much easier to pull back muscles.
To ease out the hamstrings try peddling the feet in downward facing dog –
Bending and straightening each knee in turn will ease out the backs of the legs. When comfortable with the full posture hold for 5 slow breaths. Try not to sag in the shoulder area. Push the palms and heels down and sacrum towards the ceiling.
Remember – when practising yoga at home always listen to your body, never strain and keep a smile on your face.