In The Past Week Or So I Have Started Experiencing

In the past week or so I have started experiencing pain in my left hip only when I first get up from sitting. Feels like muscle more than the joint. I am overweight, age 62, and work at a computer so I sit most of the day. It does not hurt when I walk, and usually eases when I stretch a bit, but hurts every time I get up. Sometimes aches at night when I sleep but it feels different.