Hi there. Firstly congratulations on losing an appreciable amount of weight. Keep it up and its really inspiring that you have managed to do so. Now coming to your problems.From what i have gathered after reading about your situation,you might be having a problem with your spine which may be compressing a nerve that supplies the area around the anterior aspect of the thigh, which is likely to be at the lower lumbar spine region. This problem could either be due to degenerative changes in your spine or a disc related problem. The thigh muscles are responsible for extending your knee and are part of the anti-gravity muscles that help you in standing up. Also given that you are post menopausal, i hope that you are taking supplements and adequate hormone replacement therapy. If not please consult your doctor about starting the same. Post menopausal osteoporosis can lead you to have compression fractures of the vertebrae and that may worsen an already underlying problem that you might have been having till now. If your problems are not progressively worsening, then conservative management with initial period of rest followed by physiotherapy for the back muscles such as extension exercises will be useful for you. Do remember some important danger signs, if you end up having any disturbances in your bowel/ bladder habits, such as loss of control, increasing frequency of urination or progressive weakness you will need to consult your doctor immediately. For your current problem, i suggest you get x rays of your hip joints and spine taken and get a neurological evaluation for the same. Thank you.